bluuebunny/crossref_metadata_2025 huggingface dataset:
The beta bulge: a common small unit of nonrepetitive protein structure.
Authors: Richardson J S , Getzoff E D , Richardson D C
Published: May 2006

A beta bulge is a region between two consecutive beta-type hydrogen bonds which includes two residues (positions 1 and 2) on one strand opposite a single residue (position x) on the other strand. Compared to regular beta structure, a beta bulge puts the usual alternation of side-chain direction out of register on one of the strands, introduces a slight bend in the beta sheet, and locally accentuates the usual right-handed strand twist. Almost all beta bulges are between antiparallel strands, usually between a narrow rather than a wide pair of hydrogen bonds. Ninety-one examples are listed. The two commonest types are the "classic" beta bulge, with position 1 in approximately alpha-helical conformation, and the "G1" beta bulge, with a required glycine at position 1 in approximately left-handed alpha-helical conformation, G1 bulges almost always occur in combination with a type II tight turn. The functional roles of beta bulges probably include compensating for the effects of a single-residue insertion or deletion within beta structure and providing the strong local twist required for form closed beta barrel structures.
Heat-stable enterotoxin of Escherichia coli: in vitro effects on guanylate cyclase activity, cyclic GMP concentration, and ion transport in small intestine.
Authors: Field M , Graf L H , Laird W J , Smith P L
Published: May 2006

A partially purified preparation of the heat-stable enterotoxin of Escherichia coli caused a rapid and persistent increase in electric potential difference and short-circuit current when added in vitro to the luminal surface of isolated rabbit ileal mucosa. As little as 1 ng/ml produced an easily detectable response. Under short-circuit condition, the enterotoxin abolished net Cl- absorption; this change was half that produced by theophylline, which stimulated net secretion. The enterotoxin did not change cyclic AMP concentration but caused large and persistent increases in cyclic GMP concentration. The electrical and nucleotide responses exhibited similar and unusually broad concentration-dependences and maximal effects could not be demonstrated. Theophylline elevated cyclic GMP concentration 3-fold both in the presence and absense of the enterotoxin, suggesting no effect of the toxin on cyclic GMP phosphodiesterase. Guanylate cyclase [GTP pyrophosphatelyase(cyclizing); EC 4.6.1.2] activity in a crude membrane fraction from intestinal epithelial cells was stimulated 7-fold by the enterotoxin. These results suggest that guanylate cyclase stimulation is the basis for the toxin's diarrheagenic effect.
An ordered sequence of events is required before BALB/c-3T3 cells become committed to DNA synthesis
Authors: Pledger W. J. , Stiles C. D. , Antoniades H. N. , Scher C. D.
Published: May 2006

An ordered sequence of events must be completed before cells become committed to synthesize DNA. A platelet-derived growth factor (PDGF), present in heated (100°) extracts of human platelets, induces density-inhibited BALB/c-3T3 cells to become competent to proliferate. Platelet-poor plasma induces these competent cells to leave the competence point, progress through G
0
/G
1
, and enter the S phase. Treatment of G
0
-arrested, incompetent cells with plasma, before the addition of PDGF, did not shorten the latent period for DNA synthesis or increase the rate of entry into the S phase. Growth arrest points in the plasma-dependent progression sequence were detected in G
0
/G
1
. PDGF-treated competent cells were exposed to an optimal concentration of plasma (5%) for various lengths of time and were then transferred to medium lacking plasma; the subsequent readdition of plasma stimulated the cells to enter the S phase. The lag period until DNA synthesis, in such experiments, was dictated by the length of the initial exposure to plasma. PDGF-treated competent cells that were incubated with plasma for 5 hr during the initial exposure did not leave the competence point; they began DNA synthesis 12 hr after the readdition of plasma. However, a population of cells treated with plasma for 10 hr became arrested at a point 6 hr before DNA synthesis, whereas a population treated with plasma for 12-15 hr became arrested at a point immediately before DNA synthesis. Cells remained arrested at this latter point for as long as 24 hr, and these arrested cells were not committed to DNA synthesis. The addition of plasma induced immediate entry into the S phase with an apparent first-order rate of entry being determined by the plasma concentration. This plasma-dependent commitment (transition) to DNA synthesis was blocked by cycloheximide but not by hydroxyurea. Removal of the hydroxyurea allowed cells to enter the S phase synchronously in the absence of plasma.
Low concentrations of indomethacin inhibit phospholipase A2 of rabbit polymorphonuclear leukocytes.
Authors: Kaplan L , Weiss J , Elsbach P
Published: May 2006

Inhibition of prostaglandin synthesis by indomethacin, a drug with anti-inflammatory properties, has been attributed to its action on fatty acid cyclooxygenase. However, prostaglandin synthesis would also be inhibited if precursor fatty acids were not supplied. We find that indomethacin inhibits phospholipase A2 (phosphatide 2-acylhydrolase, EC 3.1.1.4) of rabbit polymorphonuclear leukocytes in dose-dependent fashion. Inhibition is immediate and readily detected at 1 micrometer. The extent of inhibition is the same over a 10-fold range of substrate concentration and over a 500-fold range of enzyme purification. Inhibition is of the noncompetitive type, with an apparent Ki of 12 micrometer. Four other phospholipases A2--from venoms of Russell viper, Crotalus adamanteus, and bee, and from pig pancreas--are unaffected by 50 micrometer indomethacin, which inhibits leukocyte phospholipase A2 by 70%. This inhibition at low concentrations may well be important in the effects of the drug on protaglandin synthesis and inflammatory responses.
Therapy of leishmaniasis: Superior efficacies of liposome-encapsulated drugs
Authors: Alving Carl R. , Steck Edgar A. , Chapman Willie L. , Waits Virginia B. , Hendricks Larry D. , Swartz Glenn M. , Hanson William L.
Published: May 2006

Liposomes containing antimonial compounds trapped in the aqueous phase were tested in the treatment of experimental leishmaniasis. The rationale of this approach was based on the hypothesis that the liposomes and the parasite are taken up by the same cell, the reticuloendothelial cell, and we present electron microscopic evidence that supports this hypothesis. Suppression of leishmaniasis was quantified by determining the total number of parasites per liver from impression smears. When two antimonials, meglumine antimoniate and sodium stibogluconate, were encapsulated within liposomes, each was more than 700 times more active compared to either of the free (unencapsulated) drugs. After infection, if untreated, all of the hamsters eventually would die from the disease. Liposome-encapsulated meglumine antimoniate was about 330-640 times more effective in causing a drop in the death rate than was the free antimonial. The efficacy of treatment was influenced by the lipid composition and charge of the liposomes. For example, positively charged liposomes containing egg phosphatidylcholine were much less effective than negatively charged ones. In contrast, positively and negatively charged sphingomyelin liposomes were equally effective. Liposomes containing phosphatidylserine (which were negatively charged, but also had a much higher charge density) were among the less-effective preparations. Among those tested, the most consistently efficacious liposomes contained highly saturated long-chain phospholipids (eg., dipalmitoyl phosphatidylcholine), cholesterol, and a negative charge.

We conclude that liposomes may be useful as carriers of drugs to treat infectious diseases involving the reticuloendothelial system. The toxicities of antimony are very similar to those of arsenic. Encapsulation of antimonial drugs and reduction of the dose required for effective therapy should minimize such systemic toxicities as acute cardiomyopathy and toxic nephritis.
Mechanism of ultraviolet-induced mutagenesis: Extent and fidelity of
in vitro
DNA synthesis on irradiated templates
Authors: Villani Giuseppe , Boiteux Serge , Radman Miroslav
Published: May 2006

The effect of UV irradiation on the extent and fidelity of DNA synthesis
in vitro
was studied by using homopolymers and primed single-stranded ϕX174 phage DNA as substrates. Unfractionated and fractionated cell-free extracts from
Escherichia coli pol
+
and
polA1
mutants as well as purified DNA polymerase I were used as sources of enzymatic activity. (DNA polymerases, as used here, refer to deoxynucleosidetriphosphate:DNA deoxynucleotidyltransferase, EC 2.7.7.7.) The extent of inhibition of DNA synthesis on UV-irradiated ϕX174 DNA suggested that pyrimidine dimers act as an absolute block for chain elongation by DNA polymerases I and III. Experiments with an irradiated poly(dC) template failed to detect incorporation of noncomplementary bases due to pyrimidine dimers. A large increase in the turnover of nucleoside triphosphates to free monophosphates during synthesis by DNA polymerase I on irradiated ϕX174 DNA has been observed. We propose that this nucleotide turnover is due to idling by DNA polymerase (i.e., incorporation and subsequent excision of nucleotides opposite UV photolesions, by the 3′→5′ “proofreading” exonuclease) thus preventing replication past pyrimidine dimers and the potentially mutagenic event that should result. In support of this hypothesis, DNA synthesis by DNA polymerase from avian myeloblastosis virus and by mammalian DNA polymerase α, both of which are devoid of any exonuclease activity, was found to be only partially inhibited, but not blocked, by UV irradiation of the template and accompanied by an increased incorporation of noncomplementary nucleotides. It is suggested that UV mutagenesis in bacteria requires an induced modification of the cellular DNA replication machinery, possibly an inhibition of the 3′→5′ exonuclease activity associated with DNA polymerases.
ADP-ribosylation of membrane proteins catalyzed by cholera toxin: basis of the activation of adenylate cyclase.
Authors: Gill D M , Meren R
Published: May 2006

In the presence of ATP and a cytosolic factor, cholera toxin fragment A1 catalyzes the transfer of ADP-ribose from NAD to a number of soluble and membrane-bound proteins of the pigeon erythrocyte. Evidence is presented that suggests that the most readily modified membrane protein (Mr 42,000) is the adenylate cyclase-associated GTP-binding protein. Its modification by toxin is stimulated by guanine nucleotides. Adenylate cyclase activity increases in parallel with the addition of ADP-ribose to this protein and decreases in parallel with the subsequent reversal of ADP-ribosylation by toxin and nicotinamide. The protein is only accessible to toxin A subunits if the erythrocytes are lysed. When adenylate cyclase activity reaches a maximum, the number of ADP-ribose residues bound to this protein (about 1500 per cell) is similar to the reported number of beta-adrenergic receptors.
Demonstration of high-affinity folate binding activity associated with the brush border membranes of rat kidney.
Authors: Selhub J , Rosenberg I H
Published: May 2006

Folate binding activity of high affinity was identified in the particulate fractions of rat kidney homogenates. This binding activity cofractionated with alkaline phosphatase and maltase, two brush border membranes markers. With an enriched preparation of brush border membranes, freed of endogenous folate by acid treatment, the binding of [3H]olate was found to be saturable (Kb = 4.2 X 10(-11)M) and rapid. Binding was optimal at pH 6.4-7.7. At neutral pH, competition for binding with [3H]folic acid required 1.45 equivalents of pteroylheptaglutamate, 6.25 equivalents of N5-methyltetrathydrofolate, 29 equivalents of methotrexate, and 125 equivalents of N5-formyltetrahydrofolate. At alkaline pH, N5-methyltetrahydrofolate was as effective a competitor as folic acid. In view of reports that renal tubular reabsorption of folate includes an initial tight binding step, the binding activity associated with the brush border membranes may participate in this process.
Milk precipitins, circulating immune complexes, and IgA deficiency.
Authors: Cunningham-Rundles C , Brandeis W E , Good R A , Day N K
Published: May 2006

Twenty-two patients with selective IgA deficiency were studied for the presence of serum precipitins to bovine milk, bovine and fetal calf serum, and circulating immune complexes. Fifty-nine percent had circulating immune complexes, 50% had milk precipitins, 23% had precipitins to bovine serum, and 13% had precipitins to fetal calf serum. All patients with precipitating antibodies against milk or against bovine or fetal calf serum had circulating immune complexes and the precipitin titers correlated with the amount of circulating immune complexes. After one IgA-deficient patient had drunk 100 ml of milk, studies of sequential serum samples showed the presence of casein in the circulation at 60 min and the appearance of increasing amounts of immune complexes for 120 min. These findings are interpreted to indicated that in human beings the IgA system may provide a major barrier to absorption of immunogens from the gastrointestinal tract.
Failure of autologous mixed lymphocyte reactions between T and non-T cells in patients with systemic lupus erythematosus.
Authors: Sakane T , Steinberg A D , Green I
Published: May 2006

Normal human T cells proliferate vigorously when stimulated with autologous non-T cells. This autologous mixed lymphocyte reaction (MLR) between T and non-T cells was defective in patients with active systemic lupus erythematosus (SLE). In contrast, T cells and non-T cells from active SLE patients behaved normally as responding and stimulating cells, respectively, in the allogeneic MLR. The etiology of the impaired autologous MLR was further examined by studying the functional capacity of subsets of stimulating or responding cells. B cells, L cells, and monocytes from active SLE patients failed to stimulate autologous T cells but these cells effectively stimulated allogeneic T cells. Fc(IgG)+ T cells from active patients were unable to respond in both the autologous and allogeneic MLR; their Fc(IgG)-T cells responded well in the allogeneic but not in the autologous MLR. The Fc(IgG)+ T cells, but not the Fc(IgG)- T cells, from inactive SLE patients also failed to respond in the both autologous and allogeneic MLR. These studies indicate that patients with SLE have functionally defective Fc(IgG)+ T cells and a defective autologous MLR, both of which may contribute to impaired regulation of immune functions.
Structure and physiological activity of the motoneurons of the nematode Ascaris.
Authors: Stretton A O , Fishpool R M , Southgate E , Donmoyer J E , Walrond J P , Moses J E , Kass I S
Published: May 2006

The nervous system of the nematode worm Ascaris contains about 250 nerve cells; of these, the motoneurons consist of five segmental sets, each containing 11 cells. Morphologically, the motoneurons can be divided into seven different types. Their geometry is simple: some are unbranched, others have one branch point, and the most complex have two. There is no neuropil in the nerve cords; synapses are made by axo-axonal contact or onto short spines. These features enable us to study the anatomy and physiology of the system with a degree of completeness that would be difficult in other systems. The physiological activity of five of the motoneurons has been investigated, three being excitatory and two inhibitory. The excitatory motoneurons receive input from intersegmental interneurons. The inhibitory motoneurons do not receive input from the interneurons; instead they receive their input from the excitatory motoneurons in a circuit that can mediate reciprocal inhibition between the dorsal and the ventral musculature.
Presynaptic modulation of voltage-dependent Ca
2+
current: Mechanism for behavioral sensitization in
Aplysia californica
Authors: Klein Marc , Kandel Eric R.
Published: May 2006

Behavioral sensitization of the gill-withdrawal reflex of
Aplysia
is the result of a prolonged increase in transmitter release from the presynaptic terminals of sensory neurons. Earlier work suggested that this presynaptic facilitation might be mediated by a serotonin-sensitive adenylate cyclase in the sensory neuron terminals. Here we present evidence that presynaptic facilitation results from a cyclic AMP-dependent increase in the calcium current that underlies action potentials in the sensory neurons. The action potentials of sensory neuron cell bodies have, in addition to a sodium current, a calcium current that is enhanced by blocking the opposing potassium current with tetraethylammonium. Under these conditions, the action potentials show a slowly repolarizing plateau that follows the Nernst potential for a calcium electrode and serves as a sensitive assay for changes in calcium current. Stimulation of the pathway that mediates sensitization, incubation with serotonin or phosphodiesterase inhibitors, or intracellular injection of cyclic AMP produces an increase in the calcium plateau in the presence of tetraethylammonium. In addition, both before and after sensitizing stimulation, the duration of the plateau potential parallels transmitter release as measured by the amplitude of monosynaptic excitatory postsynaptic potentials evoked in the motor neurons by intracellular stimulation of single sensory neurons. These results are consistent with the idea that presynaptic facilitation is caused by a cyclic AMP-mediated increase in a voltage-sensitive calcium current in sensory neuron presynaptic terminals. This synaptic action is novel in that it can produce little or no change in the resting potential, is of long duration, and exerts its influence directly on a conductance triggered by the action potential, rather than on non-voltage-sensitive conductances, as is typical of conventional synaptic actions.
3-Hydroxy-3-methylglutaryl coenzyme A reductase: regulation of enzymatic activity by phosphorylation and dephosphorylation.
Authors: Beg Z H , Stonik J A , Brewer H B
Published: May 2006

The activity of microsomal 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMG-CoA reductase) [mevalonate:NADP+ oxidoreductase (CoA-acylating); EC 1.1.1.34] was inhibited by ATP+Mg2+. Inactivation of HMG-CoA reductase by ATP+Mg2+ was dependent on time, temperature, and ATP concentration. Incubation of microsomal HMG-CoA reductase with [gamma-32P]ATP+Mg2+ was associated with a reciprocal increase in [32P]protein-bound radioactivity and a decrease in enzymatic activity. Incubation of 32P-labeled microsomal HMG-CoA reductase with a partially purified cytosolic phosphatase resulted in a time-dependent reciprocal release of [32P]protein-bound radioactivity and reactivation of enzyme activity. Phosphorylation of HMG-CoA reductase was confirmed by immunoprecipitation of partially purified [gamma-32P]-ATP+Mg2+-inactivated microsomal HMG-CoA reductase with a reductase-specific antiserum. Sodium dodecyl sulfate electrophoresis of the [gamma-32P]immunoprecipitate revealed that the 32P radioactivity was located in the electrophoretic position of HMG-CoA reductase. These results established that the reversible inactivation of HMG-CoA reductase by ATP+Mg2+ was due to covalent modification of the enzyme by a phosphorylation-dephosphorylation reaction sequence. The existence of HMG-CoA reductase in interconvertible active and inactive forms provides a mechanism for the rapid short-term regulation of the pathway for cholesterol biosynthesis.
Association of mitochondria with microtubules in cultured cells.
Authors: Heggeness M H , Simon M , Singer S J
Published: May 2006

By indirect immunofluorescence techniques, microtubules and mitochondria were localized in normal rat kidney cells, human WI38 fibroblasts, mouse peritoneal macrophages, and a putative smooth muscle rat cell line, in monolayer culture. The mitochondria were found to be arranged along the cytoplasmic microtubules in each cell type. Disruption of the microtubules with colcemid caused a redistribution of the mitochondria in these cells. There was no correlation between the location of the mitochondria and actin-containing filaments. This evidence suggests that mitochondria are directly or indirectly associated with microtubules in these cells.
Nerve growth factor in mouse and rat serum: correlation between bioassay and radioimmunoassay determinations.
Authors: Suda K , Barde Y A , Thoenen H
Published: May 2006

High levels of nerve growth factor (NGF) determined by competition radioimmunoassay do not agree with values obtained by bioassay. This discrepancy is illustrated here with rat and mouse serum as examples in which values up to 1000 ng/ml have been found by using competition radioimmunoassays. An explanation for the discordant results is presented: serum components bind NGF with an intermediate affinity (Kd = 10(-7) M) but with a very large capacity (up to 0.5 mg of NGF per ml of rat serum). The binding of 125I-labeled NGF to serum components competes with the binding to the solid-phase antibodies (Kd = 10(-9)M) present in limiting amounts, according to the principle of competition radioimmunoassays. Thus, less radioactivity is recovered bound to the antibodies and this gives the erroneous impression that NGF is present. To overcome this difficulty, a two-site radioimmunoassay has been developed which utilizes nonlimiting numbers of antibody binding sites. This assay provides a reliable determination of NGF levels in serum and it can be shown that in rat and mouse serum (either sex) there is less than 5 ng of NGF per ml, in agreement with the results of the bioassay.
Coordination environment and fluoride binding of type 2 copper in the blue copper oxidase ceruloplasmin.
Authors: Dawson J H , Dooley D M , Gray H B
Published: May 2006

The electron paramagnetic resonance (EPR) spectra of the blue copper oxidase ceruloplasmin [ferroxidase, iron (II):oxygen oxidoreductase, EC 1.16.3.1] and of a derivative having the type I (blue) copper centers reversibly bleached are reported. The EPR spectrum of bleached ceruloplasmin has a seven-line superhyperfine structure in the g : formula: (see text) region that is attributed to the presence of three nitrogen-donor type 2 copper ligands. The EPR data suggest further that the type 2 copper in ceruloplasmin possesses a tetragonal coordination gometry. In the presence of varying amounts of fluoride, superhyperfine splitting patterns in the g : formula: (see text) region of both ceruloplasmin derivatives indicate that a maximum of two fluorides may be bound to the type 2 copper.
DNA modifying enzymes of Agrobacterium tumefaciens: effect of DNA topoisomerase, restriction endonuclease, and unique DNA endonuclease on plasmid and plant DNA.
Authors: LeBon J M , Kado C I , Rosenthal L J , Chirikjian J G
Published: May 2006

Extracts from Agrobacterium tumefaciens strain ID135 contain three enzymes that have been characterized and partially purified. The first enzyme, a DNA topoisomerase, appeared to relax only negatively twisted DNA. The second enzyme, Atu I, a type II restriction endonuclease, generated the identical DNA digestion pattern as EcoRII when several DNAs were used. The third enzyme, endonuclease A, showed a preference for superhelical DNAs as substrates. When plasmid pCK135DNA, obtained from the virulent strain IDI135 of A. tumefaciens, or plant DNA was exposed to the three enzymes, changes in DNA patterns were observed due to either conformational changes or digestion of the DNAs. These enzymes may function in vivo in the processing and incorporation of bacterial DNA in plant cells.
Resolution of the membrane moiety of the H+-ATPase complex into two kinds of subunits.
Authors: Sone N , Yoshida M , Hirata H , Kagawa Y
Published: May 2006

The H+-translocating ATPase complex from the thermophilic bacterium PS3 (TF0-F1) is composed of a water-soluble part with ATP-hydrolyzing activity (TF1) and a membrane moiety with H+-conducting activity (TF0). TF0 was obtained by treating TF0-F1 with urea and removing contaminations on a carboxymethyl-cellulose column. This TF0 contained only two kinds of subunits, band 6 protein (13,500 daltons) and band 8 protein (5400 daltons), and it was active in H+ conduction and TF1 binding when reconstituted into proteoliposomes (TF0 vesicles). The binding of TF1 to TF0 present in vesicles restored energy-transducing activities, such as ATP-32Pi exchange, dicyclohexylcarbodiimide-sensitive ATPase, and ATP-dependent enhancement of 8-anilinonaphthalene-1-sulfonate fluorescence. Treatments such as protease digestion and chemical modification with acetic anhydride, succinic anhydride, or diazobenzenesulfonic acid destroyed the TF1-binding activity, which was caused by band 6 protein. Band 8 protein was a proteolipid that reacted specifically with dicylcohexyl-carbodiimide and seemed to play a central role in H+ conduction through the membrane.
Arsoniumphospholipid in algae
Authors: Cooney Robert V. , Mumma R. O. , Benson A. A.
Published: May 2006

A novel phospholipid containing arsenic was formed by all marine algae cultured in [
74
As]arsenate. Components of the labeled algal extracts readily separated by two-dimensional paper radiochromatography. Base-catalyzed deacylation of the major lipid yielded a phosphodiester identical to one of the two major water-soluble compounds. Acid or enzymic hydrolysis of the phosphodiester produced a product identified as trimethylarsoniumalactic acid. The structure of the phospholipid therefore is
O
-phosphatidyltrimethylarsoniumlactic acid. Detoxication of arsenate by marine algae leads to accumulation of the arsoniumphospholipid as a major reservoir for arsenic. Its degradation to trimethylarsoniumbetaine, dimethylarsinic acid, methanearsonic acid, and arsenate in marine food chains and its metabolism in human beings are of considerable interest.
A macromolecular transducer as illustrated by trout hemoglobin IV.
Authors: Brunori M , Coletta M , Giardina B , Wyman J
Published: May 2006

Oxygen binding by trout Hb IV has been investigated as a function of pH up to 10 atmospheres (1 MPa) of pure O2. The results bring out an extreme proton-oxygen linkage, which gives rise to a Root effect. They are discussed in relation to the function of the hemoglobin as an oxygen pump. The system is of special interest as providing a prototype of a macromolecule acting as a transducer by coupling two allosterically linked reactions.
Amyloid fibril protein related to prealbumin in familial amyloidotic polyneuropathy.
Authors: Costa P P , Figueira A S , Bravo F R
Published: May 2006

Amyloid fibrils were concentrated from the kidney, thyroid, and peripheral nerve of six patients with familial amyloidotic polyneuropathy (FAP). The fibril concentrates were solubilized in 6 M guanidine.HCl and fractionated on Sephadex G-100 columns. The elution profile of all FAP amyloid fibril concentrates revealed a protein of apparent Mr of 14,000, designated the FAP protein, that was absent from normal human tissues treated by the same procedure and from fibrils of a primary amyloidosis liver. Antisera against whole denatured fibril concentrates prepared in rabbits reacted with the FAP protein and a component in normal human serum corresponding to prealbumin. It was further established that the FAP protein shared common antigenic determinants with human prealbumin by its reaction of identity with normal prealbumin using commercial antisera against human prealbumin. Amyloid AL or AA proteins could not be identified in FAP fibrils by sensitive immunochemical assay methods. These results suggest that the FAP protein is a unique and significant component of the FAP amyloid fibrils and that it is closely related to the 13,745 Mr prealbumin subunit.
Formation of high density lipoprotein2-like particles during lipolysis of very low density lipoproteins in vitro.
Authors: Patsch J R , Gotto A M , Olivercrona T , Eisenberg S
Published: May 2006

The effects of lipolysis of human plasma very low density lipoprotein (VLDL) on the structure and composition of high density lipoproteins (HDL) have been investigated. Lipolysis was performed in a controlled system in vitro containing VLDL (d less than 1.006 g/ml) and HDL3 (d = 1.125-1.210 g/ml) from human plasma and lipoprotein lipase (EC 3.1.1.34) purified from bovine milk. Lipolysis of VLDL caused profound changes in HDL3. Protein, phospholipid, and cholesterol liberated from VLDL during its lipolysis were transferred to the HDL3 particles. As a consequence of this in vitro transfer, the chemical composition and biophysical properties of HDL3 were substantially altered. The newly formed particles exhibited a flotation rate (F01.20) of 6.7 and a hydrated density of 1.110 g/ml. The chemical composition closely resembled that of native HDL2, and their size was slightly larger than that of the precursor HDL3. When HDL3 and postlipolysis HDL2 were subjected to ultracentrifugation under flotation velocity and equilibrium conditions, both proved to be stable particles. These results, when extrapolated to in vivo conditions, suggest an important metabolic relationship between the levels of circulating VLDL and HDL2 in plasma. This relationship now permits a reasonable explanation for numerous in vivo observations in which the levels of VLDL and HDL2 change reciprocally.
Endogenous RNA tumor viruses are activated during chemical induction of murine plasmacytomas.
Authors: Armstrong M Y , Ebenstein P , Konigsberg W H , Richards F F
Published: May 2006

Plasmacytomas are induced in BALB/c mice by the intraperitoneal injection of pristane (2,6,10,14-tetra-methylpentadecane) after a latent period of six months and more [Anderson, P. N. & Potter, M. (1969) Nature 222, 994-995]. Spleen cells mesenteric lymph node cells, thoracic lymph node cells, and peritoneal exudate cells were prepared from pristane-treated and control uninjected BALB/c mice during the course of a 10-month period, and these cell suspensions were tested for the release of infectious murine leukemia viruses. Endogenous ecotropic and xenotropic murine leukemia viruses were expressed in pristane-treated mice during the latter part of the tumor induction period, in those cell populations in which transformed plasma cells appear, namely, peritoneal exudate cells and thoracic lymph node cells. The significance of preferential expression of both ecotropic and xenotropic murine leukemia virus in target cell populations following the administration of a carcinogen is discussed in terms of the possible formation of an oncogenic variant virus.
Expression in Escherichia coli of chemically synthesized genes for human insulin.
Authors: Goeddel D V , Kleid D G , Bolivar F , Heyneker H L , Yansura D G , Crea R , Hirose T , Kraszewski A , Itakura K , Riggs A D
Published: May 2006

Synthetic genes for human insulin A and B chains were cloned separately in plasmid pBR322. The cloned synthetic genes were then fused to an Escherichia coli beta-galactosidase gene to provide efficient transcription and translation and a stable precursor protein. The insulin peptides were cleaved from beta-galactosidase, detected by radioimmunoassay, and purified. Complete purification of the A chain and partial purification of the B chain were achieved. These products were mixed, reduced, and reoxidized. The presence of insulin was detected by radioimmunoassay.
Lithium dodecyl sulfate/polyacrylamide gel electrophoresis of thylakoid membranes at 4°C: Characterizations of two additional chlorophyll a-protein complexes
Authors: Delepelaire Philippe , Chua Nam-Hai
Published: May 2006

Lithium dodecyl sulfate/polyacrylamide gel electrophoresis of
Chlamydomonas reinhardtii
thylakoid membranes at room temperature gave two chlorophyll-protein complexes, CP I and CP II, as had been reported previously. However, when the electrophoresis was performed at 4°C, there was an increase in the amount of chlorophyll associated with CP I and CP II, and in addition, three other chlorophyll-protein complexes appeared. Two of these complexes, designated CP III and CP IV, were characterized and found to be similar in their compositions. Each complex contains four to five molecules of chlorophyll a, one molecule of β-carotene, and one polypeptide chain. The apoprotein of CP III is polypeptide 5 (
M
r
50,000) and that of CP IV is polypeptide 6 (
M
r
47,000); the two polypeptides are structurally unrelated. Chlorophyll-protein complexes similar to
C. reinhardtii
CP III and CP IV were also detected in higher plants (e.g.,
Pisum sativum
). The apoproteins of the higher plant complexes are immunochemically related to those of the
C. reinhardtii
complexes, as shown by crossed immunoelectrophoresis. Absorption spectra of CP III and CP IV at -196°C revealed a component at 682 nm. This observation, together with the previous results on photosystem II mutants [Chua, N.-H. & Bennoun, P. (1975)
Proc. Natl. Acad. Sci. USA
72, 2175-2179], provides indirect evidence that CP III and CP IV may be involved in the primary photochemistry of photosystem II.
ATP-dependent renaturation of DNA catalyzed by the recA protein of Escherichia coli.
Authors: Weinstock G M , McEntee K , Lehman I R
Published: May 2006

The product of the recA gene of Escherichia coli has been purified to near-homogeneity by a simple three-step procedure. Incubation of the recA protein with complementary single strands of DNA, Mg2+, and ATP results in the rapid formation of large DNA aggregates containing many branched structures. As judged by resistance to S1 nuclease and by electron microscopy, these aggregates contain both duplex and single-stranded regions. The renaturation and aggregation of DNA catalyzed by the recA protein is coupled to the hydrolysis of ATP. The recA protein purified from a cold-sensitive recA mutant does not catalyze DNA renaturation or aggregation at 28 degrees C, but does so at 37 degrees C, a finding which correlates with the recombination defect observed in vivo and indicates that this activity is an intrinsic function of the recA protein. These results suggest that the recA protein plays a specific role in strand transfer during recombination and possibly in postreplication repair of damaged DNA.
Differences in intracellular distribution of plasminogen activator in growing, confluent, and transformed 3T3 cells.
Authors: Jaken S , Black P H
Published: May 2006

The intracellular distribution of plasminogen activator in growing, confluent, and transformed 3T3 cells was investigated by using sucrose density gradient centrifugation. In confluent cells, which do not release plasminogen activator extracellularly, most of the activity was found in a heavy membrane fraction. In growing and transformed 3T3 cells, which do release plasminogen activator extracellularly in large amounts, most of the activity was found in lighter, plasma membrane-enriched fractions. A correlation between its presence in the light membrane fractions and the ability of the cells to release the plasminogen activator extracellularly is made.
Chloroplast membrane alterations in triazine-resistant
Amaranthus retroflexus
biotypes
Authors: Arntzen Charles J. , Ditto Cathy L. , Brewer Philip E.
Published: May 2006

The effectiveness of diuron, atrazine, procyazine, and cyanazine were compared in controlling growth of redroot pigweed (
Amaranthus retroflexus
L.) in hydroponic culture. A very marked differential inhibition response was observed for atrazine between resistant and susceptible biotypes. Procyazine and cyanazine exhibited less dramatic differential responses, whereas diuron was equally effective in controlling growth in both biotypes. Photosystem II activity of chloroplasts from both triazine-resistant and triazine-susceptible biotypes was inhibited by diuron but only the chloroplasts from triazine-susceptible biotypes were inhibited significantly by atrazine. The photochemical activity of chloroplasts from triazine-resistant biotypes was partially resistant to procyazine or cyanazine inhibition. The parallel lack of diuron differential effects, partial procyazine and cyanazine differential response, and very marked atrazine differential response in both whole plant and chloroplast assays indicates that the chloroplast is the site of selective herbicide tolerance in these triazine-resistant redroot pigweed biotypes.

Photosystem II photochemical properties were characterized by analysis of chlorophyll fluorescence transients in the presence or absence of herbicides. Data with susceptible chloroplasts indicated that both diuron and atrazine inhibit electron flow very near the primary electron acceptor of photosystem II. Only diuron altered the fluorescence transient in resistant chloroplasts. In untreated preparations there were marked differences in the fast phases of the fluorescence increase in resistant vs. susceptible chloroplasts; these data are interpreted as showing that the resistant plastids have an alteration in the rate of reoxidation of the primary photosystem II electron acceptor. Electrophoretic analysis of chloroplast membrane proteins of the two biotypes showed small changes in the electrophoretic mobilities of two polypeptide species. The data provide evidence for the following herbicide resistance mechanism: genetically controlled modification of the herbicide target site.
Procollagen segment-long-spacing crystallites: their role in collagen fibrillogenesis.
Authors: Bruns R R , Hulmes D J , Therrien S F , Gross J
Published: May 2006

Naturally occurring segment-long-spacing crystallites of procollagen collagen have been found in the culture medium of fibroblasts from chick embryo tendon, human skin, and dermatosparaxic calf skin; in whole-mount preparations of cultured human skin fibroblasts; in homogenates of lathyritic chick embryo tendon, cartilage, and cornea; and in a partially purified preparation of procollagen. Bundles of similar aggregates occurred within secretory vacuoles of collagen-synthesizing fibroblasts and chondrocytes. These observations suggest that fibroblasts and chondrocytes secrete procollagen assemblies that are stable in the extracellular environment. We propose that subsequent enzymatic processing is accompanied by direct incorporation of such structures into the assembling fibril, which then may be considered as an n X 67 nm staggered array of segment-long-spacing crystallites.
Glycoprotein, elastin, and collagen secretion by rat smooth muscle cells.
Authors: Jones P A , Scott-Burden T , Gevers W
Published: May 2006

Smooth muscle cells from rat heart secreted extracellular matrix components at high rates for many generations in culture. The matrix proteins remained anchored to the culture dish and were characterized after removal of cellular material with sodium dodecyl sulfate. Sequential enzyme digestion demonstrated the presence of at least three components, including glycoprotein(s), elastin, and collagen. Prolonged extraction of the matrix with detergent under reducing conditions solubilized a fucosylated glycoprotein having an apparent molecular weight of 250,000 and two other proteins with molecular weights of 72,000 and 45,000, respectively. Sublines derived from discrete colonies of smooth muscle cells synthesized all of the matrix components, and the proportion of collagen secreted by some sublines increased with time in culture. The biosynthesis of a mixed extracellular matrix and the relationships among the component proteins were therefore studied in one system producing milligram quantities of material.
Evidence for transcriptional regulation of orotidine-5'-phosphate decarboxylase in yeast by hybridization of mRNA to the yeast structural gene cloned in Escherichia coli.
Authors: Bach M L , Lacroute F , Botstein D
Published: May 2006

From a large population of strains of Escherichia coli carrying shear fragments of yeast (Saccharomyces cerevisiae) DNA attached by in vitro recombination to the plasmid vector pMB9, two hybrid plasmids were selected that relieve the pyrimidine requirement of nonreverting pyrF mutants of E. coli. An 1100-base-pair DNA fragment common to the two complementing plasmids was recloned into another plasmid vector, pBR322; these new hybrids retained the ability to specify orotidine-5'-phosphate decarboxylase (orotidine-5'-phosphate carboxy-lyase, EC 4.1.1.23) synthesis in E. coli. Evidence is presented that this common fragment is yeast DNA and thus apparently carried the structural information for yeast orotidine-5'-phosphate decarboxylase, the product of yeast gene ura3. A hybrid plasmid containing the 1100-base-pair fragment was used to measure levels of putative ura3 mRNA from yeast cultures labeled with [3H]adenine, ura3 mRNA was unstable with an apparent half-life of 10.5 min. Under different circumstances previously shown to alter the level of orotidine-5'-phosphate decarboxylase in yeast, a coordinate variation in proportion of labeled RNA complementary to the hybrid plasmid was found. These data support the hypothesis that regulation of the ura3 gene in yeast is at the level of transcription.
Lyapounov variable: Entropy and measurement in quantum mechanics
Authors: Misra B. , Prigogine I. , Courbage M.
Published: May 2006

We discuss the question of the dynamical meaning of the second law of thermodynamics in the framework of quantum mechanics. Previous discussion of the problem in the framework of classical dynamics has shown that the second law can be given a dynamical meaning in terms of the existence of so-called Lyapounov variables—i.e., dynamical variables varying monotonically in time without becoming contradictory. It has been found that such variables can exist in an extended framework of classical dynamics, provided that the dynamical motion is suitably unstable. In this paper we begin to extend these results to quantum mechanics. It is found that no dynamical variable with the characteristic properties of nonequilibrium entropy can be defined in the
standard
formulation of quantum mechanics. However, if the Hamiltonian has certain well-defined spectral properties, such variables can be defined but only as a
nonfactorizable
superoperator. Necessary nonfactorizability of such entropy operators
M
has the consequence that they cannot preserve the class of pure states. Physically, this means that the distinguishability between pure states and corresponding mixtures must be lost in the case of a quantal system for which the algebra of observables can be extended to include a new dynamical variable representing nonequilibrium entropy. We discuss how this result leads to a solution of the quantum measurement problem. It is also found that the question of existence of entropy of superoperators
M
is closely linked to the problem of defining an operator of time in quantum mechanics.
Micronuclei of Tetrahymena contain two types of histone H3.
Authors: Allis C D , Glover C V , Gorovsky M A
Published: May 2006

Evidence is presented that micronuclei of Tetrahymena thermophila contain significant amounts of two types of histone H3. One is indistinguishable from that found in macronuclei and the other is unique to micronuclei. The micronucleus-specific H3 has a slightly faster mobility than the common H3 in three different gel systems (both of these species were artifactually lost during procedures for histone preparation in previous studies). Both micronuclear H3s appear to contain a single cysteine residue and are present in sucrose gradient-purified nucleosomes. Acid extracts from micronuclei also contain three prominent high molecular weight proteins that also were lost during previous procedures. These proteins are present in extracts from oligomers but are not observed in extracts from mononucleosomes, suggesting that they may be associated with linker regions between nucleosomes.
Construction and selection of recombinant plasmids containing full-length complementary DNAs corresponding to rat insulins I and II.
Authors: Chan S J , Noyes B E , Agarwal K L , Steiner D F
Published: May 2006

We have used a synthetic deoxydecanucleotide to generate an insulin-specific cDNA probe suitable for selecting transformants that contain nearly full-length cDNAs corresponding to the mRNAs coding for rat insulins I and II. Double-stranded cDNA was synthesized from x-ray-induced rat insulinoma poly(A)-RNA, inserted in pBR322 plasmid DNA by the homopolymeric tailing technique, and cloned in Escherichia coli chi 1776. Colony hybridization with oligonucleotide-primed cDNA yielded 16 positive clones of which 7 corresponded to rat insulin I mRNA and 9 to rat insulin II mRNA. Restriction endonuclease maps of representative clones of each group indicated that these contained the complete coding sequences, as was confirmed by nucleotide sequence analysis of the 5' region of the cloned DNA for rat insulin II. Nucleotide sequence analysis also established the amino acid sequence of the prepeptide of rat preproinsulin II. Comparison of the amino acid sequence of the prepeptides of rat preproinsulin I and II shows that three conservative amino acid substitutions have occurred in this region of the molecule.
Proton-dependent inhibition of yeast and brain hexokinases by aluminum in ATP preparations.
Authors: Womack F C , Colowick S P
Published: May 2006

The aluminum present as a contaminant in ATP preparations can cause strong inhibition of yeast hexokinase P-II activity at pH 7.0 or below but has little or no inhibitory effect at a pH of 7.5 or greater. The inhibition is reversed by citrate, 3-phosphoglycerate, malate, phosphate, and catecholamines, all of which have previously been described as activators of hexokinase at low pH. We suggest that these agents activate the enzyme only by virtue of their ability to coordinate with aluminum present in the assay system. The presence of aluminum is also responsible for the "negative cooperativity" observed at low pH with respect to Mg . ATP concentration--i.e., the inhibition by aluminum is uncompetitive at low Mg . ATP concentrations but becomes competitive at high Mg . ATP concentrations. The inhibition is thought to be due to formation of a complex of Al . ATP with the enzyme, with a dissociation constant (Ki) of 0.1 microM. Yeast hexokinase P-I is somewhat less sensitive to A1 than is hexokinase P-II, and yeast glucokinase is not detectably affected. The hexokinase in rat brain (type I) shows a pH-dependent inhibition by Al similar to that observed with the yeast hexokinases, whereas the rat muscle (type II) enzyme is less sensitive, suggesting a possible relationship to aluminum encephalopathy in man.
Assignment of the gene for cytoplasmic superoxide dismutase (
Sod-1
) to a region of chromosome 16 and of
Hprt
to a region of the X chromosome in the mouse
Authors: Francke Uta , Taggart R. Thomas
Published: May 2006

In the search for homologous chromosome regions in man and mouse, the locus for cytoplasmic superoxide dismutase (SOD-1; superoxide:superoxide oxidoreductase, EC 1.15.1.1) is of particular interest. In man, the
SOD-1
gene occupies the same subregion of chromosome 21 that causes Down syndrome when present in triplicate. Although not obviously implicated in the pathogenesis,
SOD-1
is considered to be a biochemical marker for this aneuploid condition. Using a set of 29 mouse—Chinese hamster somatic cell hybrids, we assign
Sod-1
to mouse chromosome 16. Isoelectric focusing permits distinction between mouse and Chinese hamster isozymes, and trypsin/Giemsa banding distinguishes mouse from Chinese hamster chromosomes. The mouse fibroblasts used were derived from a male mouse carrying Searle's T(X;16)16H reciprocal translocation in which chromosomes X and 16 have exchanged parts. Analysis of informative hybrids leads to regional assignment of
Sod-1
to the distal half of mouse chromosome 16 (16B4 → ter). Because the Chinese hamster cell line (380) used for cell hybridization is deficient in hypoxanthine phosphoribosyltransferase (HPRT; IMP: pyrophosphate phosphoribosyltransferase, EC 2.4.2.8), that part of the mouse X chromosome carrying the complementing
Hprt
gene can be identified by selection in hypoxanthine/aminopterin/thymidine medium and counterselection in 8-azaguanine. Mouse
Hprt
is on the X
T
translocation product containing the proximal region X cen → XD.