bluuebunny/crossref_metadata_2025 huggingface dataset:
V irus and lectin agglutination of erythrocytes: spin label study of membrane lipid-protein interactions.
Authors: Lyles D S , Landsberger F R
Published: May 2006

Techniques of spin-label electron spin resonance have been used to prove changes in the structure of the lipid phase of erythrocyte membrane after agglutination by viruses and lectins. When chicken erythrocytes are agglutinated by Sendai and influenza viruses and by the lectins concanavalin A and wheat germ agglutinin, the membrane lipid phase becomes more fluid, as detected by three different lipophilic spin-laveled probes. Colchicine, vinblastine, and tetracaine inhibit the fluidization of chicken erythrocyte membrane by Sendai virus, whereas cytochalasin B has no effect. The effect of colchicine was time dependent, the initial inhibition decreasing with longer preincubation times. Extensive treatment of erythrocytes with proteases or neuraminidase, while not altering the bilayer structure, abolishes the effect of Sendai virus on the erythrocyte membrane, suggesting that a change in the interaction of the receptor protein with the lipid phase occurs upon virus attachment. Glutaraldehyde fixation increased the structural rigidity of the chicken erythrocyte membrane and inhibited the effect of viral agglutination. No change in bilayer structure was observed upon agglutination of human erythrocytes or the isolated plasma membranes of either human or chicken erythrocytes. This result is consistent with the drug sensitivity of the effects of agglutination upon chicken erythrocytes, since human erythrocytes and isolated membranes lack microtubule-like structures.
Hormonal stimulation of DNA synthesis in primary cultures of adult rat hepatocytes.
Authors: Richman R A , Claus T H , Pilkis S J , Friedman D L
Published: May 2006

Adult rat hepatocytes have been previously isolated and maintained in monolayer culture, but attempts to stimulate DNA synthesis have been unsuccessful. Hormonal conditions are now described which induce DNA synthesis in cultured hepatocytes from partially hepatectomized rats. DNA synthesis was determined autoradiographically by the incorporation of [3H]thymidine into nuclei of morphologically distinct hepatocytes. Insulin (4-4000 nM) or epidermal growth factor (10 ng/ml) alone caused significant increases in the labeling index. The two hormones together acted synergistically to produce labeling indices of 35-50% on the third day of culture, compared with 2-7% in control cultures. The addition of glucagon (400 nM) further increased the labeling indes. Dexamethasone (80 ng/ml) inhibited DNA synthesis but, under certain conditions, enhanced cell attachment. Growth hormone and triiodothyronine had no significant effect on DNA synthesis. The mixture of epidermal growth factor, insulin, and glucagon also stimulated incorporation of [3H]thymidine into phenol-extracted DNA. Although DNA synthesis was stimulated, cell division occurred infrequently. These data suggest a prominent role for epidermal growth factor in promoting hepatic DNA synthesis by acting in concert with insulin and glucagon.
Relationship of gliadin protein components to chromosomes in hexaploid wheats (
Triticum aestivum
L.)
Authors: Kasarda Donald D. , Bernardin John E. , Qualset Calvin O.
Published: May 2006

The synthesis of the A-gliadin protein fraction derived from the endosperm of the grain of hexaploid bread wheats (
Triticum aestivum
L.), which is toxic in celiac disease, was associated with the α arm of the 6A chromosome through use of the substitution lines of “Cheyenne” chromosomes in “Chinese Spring”. The association was made through the use of ditelocentric stocks of Chinese Spring. The synthesis of many other gliadin components in the gel electrophoretic patterns of these two varieties could be associated with particular chromosomes as well. All genes detected were located in the chromosomes of homoeologous groups 1 and 6. It is possible to remove some of the proteins toxic to people with celiac disease from wheat (flour) by chromosome manipulation. If the toxic factor is not widely distributed among the storage protein components, it may be possible to produce a wheat that would be safe for celiac patients to eat.
Role of proteolytic enzymes in biological regulation (a review).
Authors: Neurath H , Walsh K A
Published: May 2006

Many enzymes, hormones, and other physiologically active proteins are synthesized as inactive precursors (zymogens) that are subsequently converted to the active form by the selective enzymatic cleavage (limited proteolysis) of peptide bonds. The ultimate agency of activating enzymatic function is limited proteolysis, either in a single activation step or in a consecutive series (cascade). The specificity of each activation reaction is determined by the complementarity of the zymogen substrate and the active site of the attacking protease. The sequence of consecutive activation reactions is regulated by the specificity of each enzyme, whereas the degree of amplification of the initial stimulus is determined by the efficiency of each activating step. Zymogen activation produces a prompt and irreversible response to a physiological stimulus, and is capable of initiating new physiological functions. Typical examples are the precesses of blood coagulation, fibrinolysis, complement activation, hormone production, metamorphosis, fertilazation, supra-molecular assembly, and digestion. The zymogens of the pancreatic serine proteases, in particular, have served as models for detailed studies of the nature of the molecular changes that are involved in the dramatic increase in enzymatic activity that ensues upon limited proteolysis of the zymogen.
Immobilization of bacterial luciferase and FMN reductase on glass rods.
Authors: Jablonski E , DeLuca M
Published: May 2006

Bacterial luciferase and NAD(P)H: FMN oxidoreductase isolated from Beneckea harveyi were covalently linked via diazotization to arylamine porous glass beads which had been cemented onto plain glass rods. These immobilized enzymes are individually active and also function to produce light via a coupled reaction utilizing NADH or NADPH. These enzymes have properties similar to the soluble forms with regard to pH and substrate optima and also exhibit linearity in peak intensity of the initial flash of light emitted as a function of NADH or NADPH concentration. Linearity with NADH is obtained in the range of 1 pmol to 50 nmol, and between 10 pmol to 200 nmol for NADPH. The bound enzymes are stable and reusable. This immobilized system offers a rapid and inexpensive m
Mechanism of action of carboxypeptidase A in ester hydrolysis.
Authors: Makinen M W , Yammura K , Kaiser E T
Published: May 2006

The reaction of carboxypeptidase A (peptidyl-L-amino-acid hydrolase; EC 3.4.12.2) with the specific ester substrate O-(trans-p-chlorocinnamoyl)-L-beta-phenyllactate has been investigated in the temperature range 25 degrees to -40 degrees with use of organic-aqueous cosolvent mixtures. In the subzero temperature range the hydrolysis reaction is characterized by a biphasic decrease in absorbance specific for the substrate. The kinetic data can be unambigously analyzed as two consecutive first-order reactions with formation of a covalent acyl-enzyme intermediate. Deacylation of the covalent intermediate is shown to be rate-limiting in the subzero temperature range, and near -60 degrees it is sufficiently stable for spectral characterization. Consideration of the structure of the active site and of the catalytically functional residues of the enzyme leads to the conclusion that the intermediate is a mixed anhydride in which the gamma-carboxylate of glutamate-270 is acylated by the substrate. The temperature dependence of the rate constants of the acylation and deacylation steps explains why the intermediate of this enzyme-catalyzed reaction is observed only at low temperatures.
Reconstitution of intramembrane particles in recombinants of erythrocyte protein band 3 and lipid: effects of spectrin-actin association.
Authors: Yu J , Branton D
Published: May 2006

The integral membrane protein Band 3 of the human erythrocyte, either purified or in a crude Triton X-100 extract of ghosts, was combined with egg lecithin in a cholate solution. During dialysis to remove cholate, lipid bilayer vesicles formed in which Band 3 existed as a dimer and in which intramembrane particles indistinguishable from those in the native membrane were exposed by freeze-fracturing. The recombinant vesicles were stable in both high and low salt concentrations, sedimented at a density that increased in prportion to their protein content, and bound spectrin-actin extracted from erythrocyte ghosts. When spectrin-actin was associated with the vesicles, the behavior of the recombinant intramembrane particles simulated that of the erythrocyte ghost intramembrane particles: they were dispersed at pH 7.6 and aggregrated at pH 5-5.5. Thus, some of the characteristics of the native membrane have been reconstituted in the recombinant.
A plasmid cloning vehicle allowing regulated expression of eukaryotic DNA in bacteria.
Authors: Polisky B , Bishop R J , Gelfand D H
Published: May 2006

We have constructed a plasmid cloning vehicle in which transcription of inserted heterologous DNA fragments can be regulated by a defined bacterial operator and promoter. The lambda plac 5 EcoRIDNA fragment containing the operator, promoter, and beta-galactosidase gene of the lactose operon was linked to the ColE1 derivative plasmid pSF2124, creating a plasmid designated pBGP100, pBGP100 contains one EcoRI site at the lac DNA/pSF2124 DNA junction and another at the lambda DAN/pSF2124 DNA junction. We deleted the latter EcoRI site to generate a plasmid (pBGP120) retaining a single EcoRI site at the lac DNA/nSF2124 DNA junction. To determine whether DNA introduced at the EcoRI site of pBGP120 was expressed under lactose control, we inserted the EcoRI fragment containing 28S ribosomal DNA of Xenopus laevis, creating the hybrid plasmid pBGP123. RNA-DNA hybridization of pulse-labeled RNA from cells containing pBGP123 showed that induction of the lac operon increases the percentage of labeled RNA complementary to Xenopus 28S DNA about 9-fold. This vehicle may be of use for production of eukaryotic gene products in bacteria.
Selective digestion of transcriptionally active ovalbumin genes from oviduct nuclei.
Authors: Garel A , Axel R
Published: May 2006

Analysis of the DNA of isolated nucleosomes suggests that virtually all genomic DNA sequences are organized in this basic chromatin subunit. In this report, we demonstrate that although histones reside on the transcriptionally active ovalbumin genes in the oviduct, the organization of proteins about this gene renders it highly sensitive to deoxyribonuclease I (deoxyribonucleate 5'-oligonucleotidohydrolase, EC 3.1.4.5). Treatment of oviduct nuclei from the laying hen with pancreatic deoxyribonuclease I results in the preferential digestion of over 70% of the ovalbumin sequences when only 10% of the total nuclear DNA has been solubilized. Treatment of liver nuclei does not reveal selective sensitivity of these genes to DNase I. Furthermore, regions of DNA not actively transcribed, such as the endogenous leukosis virus genes in the oviduct, are not selectively degraded by this enzyme. Similar digestions with micrococcal nuclease, however, reveal no specific digestion of transcriptionally active chromatin. These data confirm the observations of H. Weintraub and M. Groudine [(1976) Science 193, 848-856] and suggest we are dealing with an aspect of structure that may be necessary to permit transcription of the chromatin complex.
Collagen fibrillogenesis: intermediate aggregates and suprafibrillar order.
Authors: Trelstad R L , Hayashi K , Gross J
Published: May 2006

Polymerization of collagen in vitro has been studied with the electron microscope at early time points of fibril assembly. We have found morphologically distinct stages of aggregation, which we suggest represent successive steps in fibril formation. Linear growth of the fibril appears to occur by the tandem addition of aggregates to each other and subsequently to the ends of a subfibril; lateral growth occurs by the entwining, like a rope, of these subfibrils. Fibrillogenesis is also accompanied by extensive development of suprafibrillar order in which various patterns of parallel, spiral, and orthogonal sets of fibrils were frequently observed.
Selenium regulation of hepatic heme metabolism: induction of delta-aminolevulinate synthase and heme oxygenase.
Authors: Maines M D , Kappas A
Published: May 2006

Selenium was found to be a novel regulator of cellular heme methabolism in that the element induced both the mitochondrial enzyme delta-aminolevulinate synthase [succinyl-CoA:glycine C-succinyltransferase (decarboxylating); EC 2-3-1-37] and the microsomal enzyme heme oxygenase [heme, hydrogen-donor:oxygen oxidoreductase(alpha-methene-oxidizing, hydroxylating); EC 1-14-99-3] in liver. The effect of selenium on these enzyme activities was prompt, reaching a maximum within 2 hr after a single injection. Other changes in parameters of hepatic heme metabolism occurred after administration of the element. Thirty minutes after injection the cellular content of heme was significantly increased; however, this value slightly decreased below control values within 2 hr, coinciding with the period of rapid induction of heme oxygenase. At later peroids heme content returned to normal values. Selenium treatment caused only a slight decrease in microsomal cytochrome P-450 content. However, drug-metabolizing activity was severely inhibited by higher doses of the element. Unlike other inducers of delta-aminolevulinate synthase, which as a rule are also porphyrinogenic agents, selenium induction of this enzyme was not accompanied by an increase in the cellular content of prophyrins. When rats were pretreated with selenium 90 min before administration of heme, a potent inhibitor of delta-aminolevulinate synthase production, the inhibitory effect of heme of formation of this mitochondrial enzyme was completely blocked. Selenium, at high concentrations in vitro, was inhibitory to delta-aminolevulinate synthase activity. It is postulated that selenium may not be a direct inducer of heme oxygenase as is the case with trace metals such as cobalt, but may mediate an increase in heme oxygenase through increased production and cellular availability of "free" heme, which results from the increased heme synthetic activity of hematocytes. Subsequently, the increased heme oxygenase activity is in turn responsible for the lack of increase in the microsomal heme content, thus maintaining heme levels at normal values despite the highly increased activities of both heme oxygenase and delta-aminolevulinate synthase. It is further suggested that the increase in delta-aminolevulinate synthase activity is not due to a decreased rate of enzyme degradation or an activation of preformed enzyme, but to increased rate of synthesis of enzyme protein. Although selenium in trace amounts has been postulated to be involved in microsomal electron transfer process, the data from this study indicate that excess selenium can substantially inhibit microsomal drug metabolism.
Role of the intrinsic transglutaminase in the Ca2+-mediated crosslinking of erythrocyte proteins.
Authors: Lorand L , Weissmann L B , Epel D L , Bruner-Lorand J
Published: May 2006

Transamidase (i.e., "transglutaminase") activity of human erythrocytes, lysed by a single freezing and thawing to 37 degrees, was measured by a method of incorporating [14C]putrescine into N,N'-dimethylcasein. In the absence of added calcium ions, virtually no enzyme activity could be detected. An increase in concentration of the cation to about 0.5 mM, however, turned on the enzyme to appreciable levels of activity. Simultaneously, Ca2+ produced formation of high molecular weight, nondisulfied bonded protein polymers either directly in the lysate or in fresh cells when the cation was added together with the A23187 ionophore. The polymers could be readily identified in the isolated cell ghosts by means of disc gel electrophoresis. If the Ca2+-promoted formation of polymers was allowed to take place in the presence of 14C-putrescine, then this tracer became incorporated into the polymeric material. The incorporation indicated that polymerization occurred through gamma-glutamyl-epsilon-lysine bridtes. It is suggested that the intrinsic transamidase mediates protein crosslinking of the erythrocyte membrane whenever there is an increase in intracellular Ca2+ concentration. The presence of suitable transglutaminase substrates, e.g. histamine, inhibited crosslinking when the cells were incubated with Ca2+ and ionophore.
Regulation of the induction of colonies in vitro by normal human lymphocytes.
Authors: Gerassi E , Sachs L
Published: May 2006

Lymphocytes isolated from normal human peripheral blood can be induced to form colonies in vitro by incubation with the appropriate inducer. Phytohemagglutinin can induce colonies with T (thymus-derived) lymphocytes. Optimun colony formation with about two colonies per 10(2) peripheral blood lymphocytes was obtained by adding, in addition to phytohemagglutinin, autologous plasma, autoologous red blood cells, and fresh L-glutamine or L-cystine. In the absence of these fresh amino acids, no colonies were formed at seeding levels below 10(5) cells per 35 mm petri dish. The addition of either of these amino acids gave a 10-fold decrease in the minimum number of cells that had to be seeded for colony formation. Lipopolysaccharide did not induce the formation of colonies, but enhanced the formation of T cell colonies by phytohemagglutinin. The mixing of lymphocytes from persons with and deficient in glucose-6-phosphate-dehydrogenase (EC 1-1-1-49) has shown that phytohemagglutinin-induced colonies can be derived from single cells and are, therefore, clones. No colonies were formed by lethally irradiated cells. Incubation with pokeweed mitogen also induced the formation of colonies. With autologous plasma and autologous red blood cells, pokeweek mitogen induced about one colony per 5 X 10(3) cells seeded and no colonies at seeding levels below 10(5) cells per petri dish. The minimum number of cells needed for colony formation by pokeweed mitogen was not decreased by fresh L-glutamine or L-cystine. The results indicate that normal human lymphocytes can be cloned in vitro and that induction of these lymphocyte colonies can be regulated by lectins and other specific factors.
Concanavalin-A-induced transmembrane linkage of concanavalin A surface receptors to intracellular myosin-containing filaments.
Authors: Ash J F , Singer S J
Published: May 2006

With normal rat kidney cells in monolayer culture, we have studied the distribution on the cell surface of receptors for concanavalin A, and the distribution of the smooth muscle myosin-like protein inside the same cell, using specific fluorescence microscopic methods. The concanavalin A receptors were initially uniformly dispersed over the cell surface, but 20 min after the addition of concanavalin A at 37 degrees, the receptors showed a variety of nonuniform surface distributions, including extended parallel linear arrays. These arrays of receptors were found to be superimposed on the linear arrays of the intracellular myosin-containing filaments, indicating that a transmembrane linkage of the receptors and the filaments had occurred. This linkage required a lateral redistribution of concanavalin A receptors, since it did not occur with succinylated concanavalin A, but was subsequently induced if the cells that had been reacted with succinylated concanavalin A were then treated with antibodies to concanavalin A. The redistributions of concanavalin A receptors on the surfaces of these normal rat kidney cells, however, were much less extensive than the patching that was induced on the surfaces of the same cells infected with, and transformed by, Rous sarcoma virus.
Intraneuronal guanylyl-imidodiphosphate injection mimics long-term synaptic hyperpolarization in Aplysia.
Authors: Treistman S N , Levitan I B
Published: May 2006

The phosphodiesterase (3':5'-cyclic AMP 5'-nucleotidohydrolase, EC 3.1.4.17) inhibitor thepohylline enhances both the amplitude and duration of a long-lasting synaptic hyperpolarization in identified neuron R15 in Aplysia californica. Intraneuronal injection into R15 of glanylyl-imidodiphosphate, an adenylate cyclase [ATP pyrophosphate-lyase (cyclizing), EC 4.6.1.1] activator, results in a deep and long-lasting hyperpolarization of the cell, similar to that produced by synaptic stimulation. Biochemical analysis confirms that guanylyl-imidodiphosphate activates adenylate cyclase in Aplysia californica nervous tissue, without affecting phosphodiesterase activity. These observations suggest that adenosine 3':5'-cyclic monophosphate plays a role in long-lasting synaptic inhibition and are consistent with a post-synaptic site of action for adenosine 3':5'-cyclic monophosphate.
Diabetogenic peptide from human growth hormone: partial purification from peptic digest and long-term action in ob/ob mice.
Authors: Lostroh A J , Krahl M E
Published: May 2006

Studies in female ob/ob mice demonstrated diabetogenic properties of human growth hormone (somatotropin) and of a fragment generated therefrom by controlled digestion with pepsin; both the fragment and parent growth hormone produce long-term effects on carbohydrate metabolism; in acute glucose tolerance tests, only the fragment is active. Two nonacidic diabetogenic fractions have been separated from inactive fractions by chromatography on Bio-Gel P-6 followed by ion exchange chromatography at pH 4.3 and gel filtration on Bio-Gel P-2 and/or Sephadex G25; these active fractions exhibited multiple NH2-terminal (Lys, Phe, Leu, and Tyr). Fraction CD has these characteristics: (i) It induces glucose intolerance in fasting female ob/ob mice when injected subcutaneously in a divided dose, 15 min before and concurrently with glucose; mice injected with sufficient peptide exhibit elevated fasting glucose levels as long as 7 months after a single glucose tolerance test. (ii) It is a peptide smaller than that reported to stimulate body growth, but larger than somatostatin. This peptide, as reported earlier, does not crossreact with antiserum to human growth hormone in radioimmunoassay.
Correlation of nonorthogonality of best hybrid bond orbitals with bond strength of orthogonal orbitals
Authors: Pauling Linus
Published: May 2006

An expression is derived for the bond length of two
spd
orbitals with maximum values in two directions forming a given bond angle by consideration of the nonorthogonality integral of two best orbitals in these directions. This equation is equivalent to the expression derived by formulating the pair of orthogonal orbitals. Similar expressions are derived for
spdf
orbitals. Applications are made to icosahedral and cuboctahedral bonds and to the packing of nucleons in atomic nuclei.
Regulation of transsynaptically elicited increase of 3':5'-cyclic AMP by endogenous phosphodiesterase activator.
Authors: Gnegy M E , Costa E , Uzunov P
Published: May 2006

Experiments with cold exposure confirmed previous studies indicating that the endogenous protein acitvator of phosphodiesterase (PDEA) isolated by Cheung participates in the in vivo regulation of 3':5'-cyclic adenosine monophosphate (cAMP) in adrenal medulla. This activator of cAMP phosphodiesterase (PDE) (3':5'-cyclic-AMP 5'-nucleotidohydrolase, EC 3.1.4.17) is present in the particulate as well as the soluble fractions of rat brain. It was found that a purified cAMP-dependent protein kinase (ATP:protein phosphotransferase, EC 2.7.1.37), in the presence of ATP and cAMP, stimulates 3-fold the release of PDEA from the particulate fraction of rat brain and adrenal medulla. The substrate for this phosphorylation could be either a membrane protein that binds PDEA or PDEA itself. In vivo evidence, however, obtained by injecting rats intraventricularly with [gamma-32P]ATP, indicates that the PDEA does not contain radioactive phosphate in its structure. Also, PDEA could not be phosphorylated by protein kinase in vitro. The following mechanism is postulated: when the intracellular content of cAMP increases it activates a protein kinase which phosphorylates a PDEA-binding membrane protein and releases PDEA. In turn this binds to activator-deficient high Km PDE and decreases its Km to facilitate the hydrolysis of the increased concentration of cAMP.
A method for determination of the in situ distribution of chromosomal proteins.
Authors: Silver L M , Elgin S C
Published: May 2006

A technique has been developed for "staining" cytological preparations by indirect immunofluorescent methods that permits determination of the in situ distribution of chromosomal proteins. The method is particularly oriented to the use of polytene chromosome squashes from Drosophila salivary glands. Control experiments indicate that the fixation methods used allow little or no extraction or rearrangement of the chromosomal proteins. The results obtained demonstrate the specific in vivo chromosomal locations of nonhistone proteins purified from isolated chromatin. The technique is apparently capable of resolution at the level of the chromomere or band, the unit of genetic organization in Drosophila.
Mechanistic studies of glutamine synthetase from Escherichia coli: kinetic evidence for two reaction intermediates in biosynthetic reaction.
Authors: Rhee S G , Chock P B
Published: May 2006

Fast reaction techniques were used to study the kinetics of protein fluorescence intensity changes that are associated with the reactions of unadenylylated Escherichia coli glutamine synthetase [L-glutamate: ammonia ligase (ADP-forming), EC 6.3.1.2] with its substrates. It was established that the synthesis of glutamine occurs by a stepwise mechanism. During the catalytic process two fluorometrically distinct intermediates were observed. Both forward and reverse rate constants which lead to the formation and consumption of these intermediates were evaluated. The catalytic rate constant, kc, which was calculated from these rate constants agrees well with the values of kc which were determined by direct measurement of the overall biosynthetic activities by means of stopped-flow technique or the steady-state assay method.
Lack of ribosomal protein S1 in Bacillus stearothermophilus.
Authors: Isono K , Isono S
Published: May 2006

The 30S ribosomal subunit of Bacillus stearothermophilus migrated as a single band when electrophoresed on agarose-acrylamide composite gels. The addition of the ribosomal protein S1 purified from Escherichia coli resulted in the appearance of an additional band migrating more slowly; 14C-labeled S1 of E. coli was shown to be associated only with this form. Antibody against E. coli protein S1 did not crossreact with either the total 30S ribosomal proteins or the postribosomal supernatant from B. stearothermophilus. These results indicate that B. stearothermophilus lacks a protein equivalent to E. coli S1 and may explain our previous finding [Eur. J. Biochem. 56, 15-22 (1975) that E. coli S1 greatly stimulated the translation by B. stearothermophilus ribosomes of f2 phage RNA.
Antibody differentiation: apparent sequence identity between variable regions shared by IgA and IgG immunoglobulins.
Authors: Sledge C , Fair D S , Black B , Krueger R G , Hood L
Published: May 2006

We have analyzed a pair of human myeloma immunoglobulins (biclonal proteins) of the IgG and IgA classes from a single patient, GR. The light chains are identical in amino-acid sequence over 40 residues at their NH2-terminus, hwereas the heavy chains are identical throughout 45 residues of their NH2-terminus. Additional chemical and serological studies suggest the light chains and variable regions of the heavy chains (VH) are very similar, if not identical. The implications of these and of other published studies are discussed with regard to (i) the association of one VH region with multiple constant regions of the heavy chain (CH regions), (ii) two alternative types of V-C joining mechanisms, (iii) the differentiation of antibody-producing cells, and (iv) three categories of biclonal immunoglobulins.
Photoprotection by carotenoid pigments in the copepod Diaptomus nevadensis.
Authors: Hairston N C
Published: May 2006

Individuals of the copepod Diaptomus nevadensis that contain high concentrations of carotenoids survive significantly better in natural intensities of visible light than less pigmented copepods. Vertical migration and behavior in light of different wave lengths are related to the degree of pigmentation.
Electron probe x-ray analysis of single ferritin molecules.
Authors: Shuman H , Somlyo A P
Published: May 2006

Single molecules and groups of two or three ferritin molecules were subjected to electron probe x-ray microanalysis in a transmission electron microscope equipped with a liquid nitrogen cooled stage. Significant Fe Kalpha peaks were generated during 100-sec counts when single ferritin molecules were excited with a probe current of 0.35 nA/60 nm spot, less than the maximal current available in a thermionic gun. There was a linear relationship between the number of ferritin molecules analyzed and count rates. The experimental results are compared to the theoretically calculated Fe Kalpha yields and to the results of Isaacson and Johnson [(1975) Ultramicroscopy I, 33-52] with electron energy loss analysis. We conclude that current state of the art electron probe x-ray analysis can realize the theoretically predicted sensitivity of the method, and estimate 0.9 X 10(-19) g of Fe as the minimal mass detectable with maximal (thermionic) probe current during a 100-sec count and with 95% confidence.
Distribution of Ia-like molecules on the surface of normal and leukemic human cells.
Authors: Schlossman S F , Chess L , Humphreys R E , Strominger J L
Published: May 2006

Antiserum to a glycoprotein antigen complex of 23,000 and 30,000 dalton subunits (p23,30), isolated and purified from a human lymphoblastoid B cell line, was shown to be highly specific for human bursal-equivalent-processed (B) cells, reactive with 15-20% of human Null cells, but completely unreactive with human thymus-processed (T) cells. The p23,30 antigen is widely distributed on chronic lymphatic leukemic cells, 85% of acute lymphatic leukemic cells, all acute myelogenous leukemic cells, but not on chronic myelogenous leukemic cells. A rabbit antiserum specific for normal human thymocytes has also been prepared; it is reactive only with precisely that subset of acute lymphatic leukemic cells (15%) whose members do not have p23,30 on their surfaces.
Angles between orthogonal
spd
bond orbitals with maximum strength
Authors: Pauling Linus
Published: May 2006

An equation is derived for values of bond angles for two equivalent best
spd
hybrid bond orbitals with given amounts of
s, p
, and
d
character, and is applied in the discussion of structures of transargononic compounds, including the xenon and halogen fluorides. Bond orbitals with a rather small amount of
d
character tend to lie at angles 90° and 180°, and those with a larger amount, at somewhat smaller angles.
2-diazo-3,3,3-trifluoropropionyl chloride: reagent for photoaffinity labeling.
Authors: Chowdhry V , Vaughan R , Westheimer F H
Published: May 2006

2-Diazo-3,3,3-trifluoropropionyl chloride has been synthesized from trifluorodiazoethane and phosgene. Its derivatives are acid stable, can be used to label enzymes, and undergo photolysis with substantially less rearrangement than do derivatives of other known diazoacyl reagents designed for photoaffinity labeling. In particular, the diazotrifluoropropionyl thioester of methyl N-acetylcysteine undergoes photolysis in methanol with about 40% insertion into the - OH bond of the solvent; by contrast, photolysis of other diazoacyl thioesters gives substantially quantitative Wolff rearrangement. The trifluoro compounds hold promise for the photoaffinity labeling of thiols.
An extension of the concept of inertial frame and of Lorentz transformation
Authors: Kerner Edward H.
Published: May 2006

It is shown how particular kinds of fractional-linear (or projective) transformations generalize the notion of inertial frame in that they ensure that free-particle motion goes over into free-particle motion. A ten-parameter group of such transformations is produced which generalize Lorentz transformations, and which involve besides
c
(velocity of light) a new fundamental length
b
; they encompass the ordinary Lorentz group in the limit that
b
becomes infinite. These extended Lorentz transformations are most simply understood as a type of rotation in the space of homogeneous coordinates, a rotation that unifies 3-space rotations, frame-shifts to moving frames, and space- as well as time-translations. The structure of the invariant differential line element and of the wave operator that generalize those of special relativity are discussed, and implications for the possible revision of usual physical statements are pointed out.
Cobalt inhibition of synthesis and induction of delta-aminolevulinate synthase in liver.
Authors: Maines M D , Janousĕk V , Tomio J M , Kappas A
Published: May 2006

Cobalt has complex actions on the metabolism of heme in the liver. In this organ the metal potently induces heme oxygenase (EC 1.14.99.3), and decreases cellular heme and hemoprotein content. The metal also displays biphasic effects on hepatic heme synthesis. These effects are reflected in the ability of cobalt to initially inhibit synthesis of delta-aminolevulinate synthase [succinyl-CoA:glycine C-succinyltransferase (decarboxylating) EC 2.3.1.37], the rate limiting enzyme of the heme pathway, following which a later enhanced rate of formation of this enzyme occurs. In this study, cobalt was shown to block almost entirely the ability of the barbiturate analogue allylisopropylacetamide to induce delta-aminolevulinate synthase in liver. The blocking effect of cobalt on the otherwise potent enzyme inducing action of this drug was time-dependent; if the metal was injected 30 min prior to allylisopropylacetamide, inhibition of enzyme induction was complete. When the metal was administered 1.5 or more hours after allylisopropylacetamide, inhibition of enzyme induction was incomplete. Cobalt did not block the ability of the drug to directly degrade heme to "green pigment" thus the enzyme inducing action of allylisopropylacetamide and its degradative action on heme are separately mediated.
Electron microscopy of gene regulation: The
L
-arabinose operon
Authors: Hirsh Jay , Schleif Robert
Published: May 2006

Using high magnification electron microscopy, we have observed protein complexes specifically bound to homogeneous DNA fragments containing the regulatory region of the
Escherichia coli
L
-arabinose operon. Formation of detectable complexes on the DNA requires
araC
protein, catabolite gene activator protein, and RNA polymerase (nucleotidyltransferase). These protein–DNA complexes appear to be involved in regulation of the operon. Incubation of the proteins and DNA under inducing conditions leads to formation of a complex that appears to be capable of transcription, whereas incubation of the proteins and DNA under repressing conditions leads to formation of a different complex incapable of transcription. Using three overlapping DNA fragments, we located the sites of complex formation on the DNA. The complexes are formed on sequences 108 base pairs apart, an unexpectedly large distance.
Nuclear magnetic resonance study of heme-heme interaction in hemoglobin M Milwaukee: implications concerning the mechanism of cooperative ligand binding in normal hemoglobin.
Authors: Fung L W , Minton A P , Ho C
Published: May 2006

Hemoglobin M Milwaukee (beta 67E11 val leads to Glu) is a naturally occurring valency hybrid containing two permanently oxidized hemes in the beta-chains. In this mutant, the two abnormal beta-chains cannot combine with oxygen, whereas the two alpha-chains are normal and can combine with oxygen cooperatively with a Hill coefficient of approximately 1.3. High-resolution proton nuclear magnetic resonance spectroscopy at 250 MHz has been used to investigate the hyperfine shifted resonances of the abnormal ferric beta-chains of Hb M Milwaukee over the spectral region from -30 to -60 parts per million from water at pD 7 and 30 degrees.
Inelastic electron tunneling spectroscopy of nucleic acid derivatives.
Authors: Clark J M , Coleman R V
Published: May 2006

Inelastic electron tunneling spectra of nucleosides and nucleotides are presented which show that detailed information on the vibrational spectra of these molecules can be obtained from a few micrograms of material. A series of studies on adenine derivatives demonstrates that unambiguous identification of a large number of slightly different derivatives can be carried out by means of this technique.
Lipid vesicles as carriers for introducing materials into cultured cells: influence of vesicle lipid composition on mechanism(s) of vesicle incorporation into cells.
Authors: Poste G , Papahadjopoulos D
Published: May 2006

The mechanisms involved in the uptake of uni- and multi-lamellar lipid vesicles by BALB/c mouse 3T3 cells have been investigated. Vesicles are incorporated into cells both by endocytosis and by a nonendocytotic mechanism which we propose involves fusion of vesicles with the plasma membrane. The nonendocytotic pathway predominates in the uptake of negatively charged vesicles composed of phospholipids that are "fluid" (phosphatidylserine/phosphatidylcholine) at 37 degrees. Neutral fluid vesicles (phosphatidylcholine) and negatively charged vesicles prepared from "solid" phospholipids (phosphatidylserine/distearylphosphatidylcholine/dipalmitoylphosphatidylcholine) are instead incorporated largely by endocytosis. Uptake of the latter classes of vesicle is reduced (80-90% inhibition) by inhibitors of cellular energy metabolism and by cytochalasin B.
An evaluation of messenger RNA competition in the shutoff of human interferon production.
Authors: Sehgal P B , Tamm I
Published: May 2006

The process that shuts off poly(I)-poly(C)-induced interferon production in a strain of diploid human fibroblasts (FS-4)-involves the synthesis of new RNA, presumably nuclear heterogeneous RNA. When cultures in the shutoff phase of interferon production are treated with actinomycin D (5 mug/ml) or 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole (DRB 40 muM), the rate of interferon production continues to decline for a further 3-4 hr, but then tends to level off. The treated cultures maintain interferon production at a reduced level for at least 10 hr. The residual rate of interferon production is higher in cultures which received actinomycin D or DRB early in the shutoff phase as compared to the rate in cultures treated late.
dunce, a mutant of Drosophila deficient in learning.
Authors: Dudai Y , Jan Y N , Byers D , Quinn W G , Benzer S
Published: May 2006

Normal Drosophilia learn to avoid an odorant associated with electric shock. An X-linked mutant, dunce, has been isolated that fails to display this learning in spite of being able to sense the odorant and electric shock and showing essentially normal behavior in other respects.
Inhibition of arachidonic acid release from cells as the biochemical action of anti-inflammatory corticosteroids.
Authors: Hong S L , Levine L
Published: May 2006

Serum stimulates the production of prostaglandins by transformed mouse fibroblasts. Hydrocortisone (cortisol) inhibits this stimulation. The half-maximal inhibition occurs at 6x10-9 M. Studies with cells labeled with [3H]arachidonic acid in their lipids show that the stimulation by serum results in the release of arachidonic acid from the cellular lipids, mostly phospholipids. Hydrocrotisone inhibits this release but does not inhibit the production of prostaglandins from exogenously supplied arachidonic acid. This inhibition of arachidonic acid release from phospholipids may be the mechanism for the anti-inflammatory action of corticosteroids.
Guanidine-unfolded state of ribonuclease A contains both fast- and slow-refolding species.
Authors: Garel J R , Nall B T , Baldwin R L
Published: May 2006

The kinetics of the refolding reaction of ribonuclease A from high concentrations of guanidine hydrochloride or urea are biphasic, and show two refolding reactions whose rates differ 450-fold at pH 5.8 and 25 degrees. Measurements of cytidine 2'-phosphate binding during refolding, after stopped-flow dilution of guanidine hydrochloride (Gdn.HCl) or urea, show that functional bovine pancreatic ribonuclease A (RNase A; ribonucleate 3'-pyrimidino-oligonucleotidohydrolase, EC 3.1.4.22) is formed in both the fast and slow phases of the refolding process. We conclude that the guanidine-unfolded state of RNase A is an equilibrium mixture of fast- and slow-refolding species, as was found previously for the heat-unfolded state at low pH. The fraction of the fast-refolding species in guanidine or urea-unfolded RNase A is the same as that in the heat-unfolded protein at pH 2. Previous work has shown that the fast-refolding species disappears as the pH is raised from 3 to 5 for heat-unfolded RNase A. This pH effect is not present in refolding from concentrated Gdn.HCl solutions: the same proportion of the fast-refolding species is found from pH 2 to pH 6, and also from 2 M to 6 M Gdn.HCl at pH 5.8. We conclude that the same proportion of the fast-refolding species is present at equilibrium whenever the residual structure in unfolded RNase A is reduced to a low level, and that the structural difference between the fast-refolding and slow-refolding species of RNase A lies in the configuration of the random coil polypeptide chain.
Solenoidal model for superstructure in chromatin.
Authors: Finch J T , Klug A
Published: May 2006

Chromatin prepared by brief digestion of nuclei with micrococcal nuclease, and extracted in 0.2 mM EDTA, appears in the electron microscope as filaments of about 100 A diameter which coil loosely. In 0.2 mM Mg++ these "nucleofilaments" condense into a supercoil or solenoidal structure of pitch about 110 A corresponding to the diameter of a nucleofilament. It is proposed that the x-ray reflections at orders of 110 A observed in chromatin originate in the spacing between turns of the solenoid rather than that between nucleosomes along the nucleofilament. The solenoidal structure appears to need histone H1 for its stabilization. Under certain conditions, isolated nucleosomes can also aggregate into a similar structure. The solenoidal structure can be correlated with the "thread" of diameter about 300 A observed by other workers in nuclei.
Phenotypic transformation of clonal myogenic cells to cells resembling chondrocytes.
Authors: Schubert D , Lacorbiere M
Published: May 2006

The nicotinamide analogue 6-aminonicotinamide and dibutyryl 3':5'-cAMP inhibit myogenesis in a clonal rat cell line from skeletal muscle. Both reagents produce a similar morphological response in the cells, and stimulate collagen and glycosaminoglycan synthesis. These data suggest that 6-aminonicotinamide and dibutyryl cAMP induce a phenotypic transformation of myogenic cells to cells that share many characteristics with chondrocytes.
Ontogeny of murine B lymphocytes: sequence of B-cell differentiation from surface-immunoglobulin-negative precursors to plasma cells.
Authors: Hämmerling U , Chin A F , Abbott J
Published: May 2006

Among bone-marrow-derived (B) lymphocytes exist subpopulations of cells that can be induced to express the markers: surface immunoglobulin (Ig), the antigen associated with the immune response gene (Ia), and the receptor for the third complement component (CR). Inducible cells for the first two markers are found in bone marrow, and inducible cells for all three are in spleen. Experiments were designed to determine whether induction involves a single precursor cell population that on triggering with lipopolysaccharide expresses all three surface markers, or three separate precursor cell populations each of which expresses a single marker. Specific B cell subpopulations were eliminated by treatment with anti-Ig or anti-Ia and complement, or by rosette formation with erythrocytes-antibody-complement followed by differential centrifugation, and surviving cells were subsequently tested for inducibility of the three B cell markers. After anti-Ig cytolysis only Ig, but not Ia and CR, could be induced, implying that the Ia- and the CR-inducible cells are Ig+. Similarly, after anti-Ia cytolysis Ig and Ia but not CR could be induced. Thus, CR-inducible cells must have the Ig+Ia+ phenotype. Elimination of CR+ cells did not affect the induction of Ig, Ia, or CR from their precursors. None of the three elimination experiments affected the conversion of prothymocytes (Thy-1-) to thymocytes (Thy-1+). From these results we propose the hypothesis that the differentiation of B lymphocytes proceeds through at least four distinct stages characterized by the following phenotypes: Ig-Ia-CR- leads to Ig+Ia-CR- leads to Ig+Ia+CR- leads to Ig+Ia+CR+.
Release by human chromosome 3 of the block at G1 of the cell cycle, in hybrids between tsAF8 hamster and human cells.
Authors: Ming P M , Chang H L , Baserga R
Published: May 2006

A temperature-sensitive mutant of Syrian hamster cells, AF8 was fused with simian-virus-40-transformed Lesch-Nyhan fibroblasts; LNSV, in the presence of beta-propiolactone-inactivated Sendai virus. The AF8 cells grow well at 33.5 degrees but are arrested in mid G1 period when shifted to 39 degrees. The LNSV cells are deficient in hypoxanthine guanine phosphoribosyltransferase. The hybrid clones were selected in hypoxanthine-aminopterin-thymidine medium at 39 degrees. A total of 20 clones was isolated and karyotyped. All clones contained most of the hamster chromosomes and one to eight human chromosomes. The preferential retention of human chromosome 3 was observed in 100% of the metaphases of all clones. In nine of the clones, the only human chromosome present was chromosome 3. The results indicate that human chromosome 3 is responsible for conferring to the hybrid cells the ability to grow at nonpermissive temperature for AF8 cells, i.e., the ability to overcome the G1 block. These findings, together with other reports in the cell cycle may be regulated by genes located on different chromosomes.
Mapping of the influenza virus genome: identification of the hemagglutinin and the neuraminidase genes.
Authors: Palese P , Schulman J L
Published: May 2006

Polyacrylamide gel electrophoresis of the RNA of influenza A/PR/8/34 (H0N1) and A/Hong Kong/8/68 (H3N2) viruses and recombinant viruses derived from them revealed that each contains eight RNA segments, the fourth of which codes for hemagglutinin. (The largest RNA of the segmented genome is counted as band 1.) The neuraminidase gene was identified as the sixth segment in the RNA pattern of influenza A/PR8 virus and as the fifth segment of A/Hong Kong virus. The molecular weights of the RNAs for the hemagglutinin and the neuraminidase genes lie in the range of 600,000-700,000.
Purification and properties of a DNA-binding protein with characteristics expected for the Cro protein of bacteriophage lambda, a repressor essential for lytic growth.
Authors: Folkmanis A , Takeda Y , Simuth J , Gussin G , Echols H
Published: May 2006

The Cro protein specified by bacteriophage lambda is a repressor essential for normal lytic growth of the virus, thus having a physiological role distinct from that of cI, the repressor that maintains lysogeny. We have purified a lambda-specific DNA-binding protein with the requirements for synthesis and biochemical activities expected for Cro protein from studies in vivo. As isolated, the protein appears to be a dimer of molecular weight approximately 18,000 with DNA-binding properties that are very similar, but not identical, to those of the cI protein. We infer that bacteriophage lambda uses the same regulatory region of DNA for two different DNA-binding repressor proteins with subtle differences in binding activity specialized for different physiological roles.