bluuebunny/crossref_metadata_2025 huggingface dataset:
The law of perceptual stability: Well-definedness and validity
Authors: Shiman Leon G.
Published: May 2006

Axiomatic foundations for a theory of perception have been given in a prior communication [Shiman, L. G. (1978)
Proc. Natl. Acad. Sci. USA
75, 2049-2053]. The theory is based on mathematically characterized stable images. Stable images model subjective (psychological) states of observers. We showed there is a universal procedure by which such stable images can be assigned to objects of perception (icons), employing observer-dependent perceptual judgements.

We construct an abstract model for an icon from the mathematical structure of a stable image that has been assigned to it. We identify the model with the icon. By identifying the model with the object of perception, we can analyze perception of the icon in terms of the mathematical properties of its associated stable images. Thus subjective phenomena, in this mathematical form, can be used to analyze the mechanisms of sensory processes.

Grounds for validity of the stability law are given. The procedures are demonstrably universal. A stable image, although subjectively derived from an icon, is a mathematical entity, and has therefore objective status. Stable images give a natural and potentially complete (mathematical) classification of icons, along nontraditional lines, which includes a classification and account of many well-known “visual illusions.”

Extension of this (
static
) theory to include time-dependent (
kinetic
) cases is outlined. We consider grammar for vision, semantics, and the role of stability theory in constructing a unified theory of vision and natural languages.
Sugar pucker geometries at the intercalation site of propidium diiodide into miniature RNA and DNA duplexes in solution.
Authors: Patel D J , Shen C
Published: May 2006

We have evaluated the sugar pucker geometry at the intercalation site of propidium diiodide into the self-complementary dinucleoside monophosphate duplexes cytidylylguanosine and deoxycytidylyldeoxyguanosine as a function of the nucleotide/drug ratio in aqueous solution. Our solution results support the observation by Sobell and coworkers [Sobell, H.M., Tsai, C.C., Jain, S.C. & Gilbert, S.G. (1977) J. Mol. Biol. 114, 333--365] of a C3' endo (3'-5')C2' endo sugar pucker geometry in the 2:2 intercalation complex of ethidium bromide into the iodocytidylylguanosine duplex in the crystalline state. We demonstrate further that the mixed sugar pucker observed for the intercalation of propidium diiodide into the miniature RNA duplex in solution persists in the intercalative complex of this trypanocidal drug into the corresponding miniature DNA duplex in solution.
Incompressible minimal surfaces, three-dimensional manifolds with nonnegative scalar curvature, and the positive mass conjecture in general relativity
Authors: Schoen Richard , Yau Shing-Tung
Published: May 2006

We study three-dimensional Riemannian manifolds with nonnegative scalar curvature. We find new topological obstruction for such manifolds. Our method turns out to be useful in studying the positive mass conjecture in general relativity.
Selective complexing of the "nuclear" 5S estradiol receptor by a serum component, 5S-CA.
Authors: Fox T O
Published: May 2006

A component present in several sera interacts selectively with the 5S "nuclear" form of estradiol receptor but not with the 4S "cytosol" form. This component is therefore referred to as "5S-complexing activity (5S-CA)." This selective interaction occurs with 5S receptor from mouse, calf, or rat. In addition, 5S-CA recognizes the nuclear form of the receptor from hypothalamic as well as uterine tissue Thus, 5S-CA indicates a general similarity in the chemical nature of 5S nuclear receptors prepared from several sources. Using 5S-CA as a chemical probe for the nuclear form of the estradiol receptor, I have shown the chemical as well as physical similarity of 5S receptors prepared in vivo (by injection of [3H]estradiol and subsequent isolation from nuclear/myofibrillar extracts) and in vitro (by labeling of cytoplasmic extracts and subsequent chromatography on columns of DNA-cellulose). These results indicate a distinctive chemical property of nuclear 5S forms of estradiol receptor. The data are interpreted with regard to models for 5S receptor formation. 5S-CA was found in sera from animals immunized against various antigens. The importance of testing for 5S-CA in antisera directed against steroid derivatives, steroid receptors, and other steroid-binding proteins is discussed.
Nitrogenase and nitrogenase reductase associate and dissociate with each catalytic cycle.
Authors: Hageman R V , Burris R H
Published: May 2006

Nitrogenase and nitrogenase reductase dissociate after each electron is transferred between them, as shown by the occurrence of a lag phase approximately as long as the average turnover time of nitrogenase before hydrogen evolution occurs. Because nitrogenase was present in the reaction mixture in large excess over nitrogenase reductase, the electrons donated by nitrogenase reductase must have been distributed randomly over all of the nitrogenase present. This is accomplished by nitrogenase reductase molecules associating randomly with nitrogenase molecules for each cycle of electrons transferred. The fact that ATP is hydrolyzed without a lag indicates both that electron transfer occurs during the lag and the ATP hydrolysis is coupled to electron transfer from nitrogenase reductase to nitrogenase and not to substrate reduction. The observations support the suggestion that it now is desirable to alter nomenclature to designate the MoFe protein as nitrogenase and the Fe protein as nitrogenase reductase.
Vasoactive intestinal peptide: A potent stimulator of adenosine 3′:5′-cyclic monophosphate accumulation in gut carcinoma cell lines in culture
Authors: Laburthe M. , Rousset M. , Boissard C. , Chevalier G. , Zweibaum A. , Rosselin G.
Published: May 2006

Vasoactive intestinal peptide (VIP) is a potent and efficient stimulator of adenosine 3′:5′-cyclic monophosphate (cAMP) accumulation in a human colon carcinoma cell line, HT 29. cAMP accumulation is sensitive to a concentration of VIP as low as 3×10
-12
M. Maximum VIP-induced cAMP levels were observed with 10
-9
M VIP and are about 200 times above the basal levels. Half-maximum cAMP production was obtained at 3×10
-10
M VIP.
125
I-Labeled VIP was found to bind to HT 29 cells; this binding was competitively inhibited by concentrations of unlabeled VIP between 10
-10
and 10
-7
M. Half-maximum inhibition of binding was observed with 2×10
-9
M VIP. Secretin also stimulated cAMP accumulation in HT 29 cells, but its effectiveness was 1/1000 that of VIP. The other peptides tested at 10
-7
M, such as insulin, glucagon, bovine pancreatic polypeptide, somatostatin, octapeptide of cholecystokinin, neurotensin, and substance P, did not stimulate cAMP accumulation. Prostaglandin E
1
and catecholamines stimulated cAMP production but were 1/2.3 and 1/5.5 as efficient as VIP, respectively. Another malignant cell line from the gut, the human rectal tumor cell line HRT 18, is also sensitive to VIP. In HRT 18 cells, VIP stimulated cAMP accumulation with a maximal effect at 10
-8
M; half-maximum stimulation was observed at about 10
-9
M. These results demonstrate the presence of VIP receptors in two malignant human intestinal cell lines (HT 29 and HRT 18) in culture and provide a model for studying the action of VIP on cell proliferation.
In vitro differentiation of a fast Na+ conductance in embryonic heart cell aggregates.
Authors: Nathan R D , DeHaan R L
Published: May 2006

Aggregates of 3-day chick cardiac myocytes, after 2 days of gyration culture, lack a tetrodotoxin-sensitive, fast Na+ conductance. After 2--3 additional days in vitro these aggregates were shown by three different criteria to have developed such a conductance mechanism: (a) action potential upstroke velocities greater than 90 V/sec; (b) suppression of spontaneous activity by tetrodotoxin; and (c) presence of a fast component of inward current recorded during voltage clamp. These membrane properties were similar to those of aggregates derived from 7-day hearts that had developed in ovo. The differentiation of fast Na+ conductance channels was a dependent upon active protein synthesis but not upon the presence of exogenous macromolecules.
De
novo
induction of a gene product during heterologous epithelial-mesenchymal interactions
in vitro
Authors: Hata Ryu-ichiro , Slavkin Harold C.
Published: May 2006

Mesenchymal specification of epithelial cytodifferentiation and morphogenesis has been considered to be a general feature of various epithelial-mesenchymal interacting systems (e.g., salivary gland, mammary gland, feather, hair, and tooth morphogenesis). In contrast, we have demonstrated that a mesenchyme can be induced by a heterologous epithelium to synthesize in quantity a specific gene product(s) unorthodox to the organ from which the mesenchyme was taken. Stage 22-23 avian limb bud epithelium induced 17-day embryonic mouse tooth mesenchyme to differentiate into cartilage. Peptide analysis (cyanogen bromide cleavage after purification of extracted collagen chains) demonstrated that heterologous tissue recombinations produced type II collagen [α(II)]
3
(i.e., cartilage-type) in addition to type I collagen [α(I)]
2
α
2
. Intact or reconstituted mouse molar tooth organs synthesized type I collagen and type I trimer [α(I)]
3
collagen. Immunohistochemical criteria using anti-type II collagen antibodies identified type II collagen in cartilage-like matrix within the mesenchymal component of heterologous tissue recombinants. Cartilage has never been described during
in vivo
or
in vitro
tooth tissue differentiation or associated with the pathology of dental papilla mesenchyme. These results support the hypothesis that epithelial-mesenchymal interactions during embryonic development can selectively induce
de novo
synthesis of unique gene products.
Potentiation, desensitization, and inversion of response in bacterial sensing of chemical stimuli.
Authors: Rubik B A , Koshland D E
Published: May 2006

Behavior patterns of chemotactic mutants of Salmonella typhimurium were compared to those of the wild type by using the quantitative tumble frequency assay. Some cheU mutants were completely inverted in their responses--e.g., attractants produce responses expected for repellents and repellents produce responses expected for attractants. Still others swam smoothly and did not respond to any stimuli. Mutants of other complementation groups were found to exhibit exact additivity or potentiation in response to multiple stimuli whereas the wild type showed desensitization. The results suggest that the cheU gene product acts as a switch at the interface between the sensing system and the motor response. The system is finely tuned so that changes in individual proteins can produce potentiation, desensitization, exact additivity, or inversion of responses.
[Met5]Enkephalin content in brain regions of rats treated with lithium.
Authors: Gillin J C , Hong J S , Yang H Y , Costa E
Published: May 2006

In rats, chronic treatment with lithium elicits a dose-dependent increase in the [Met5]enkephalin content of nucleus caudatus and globus pallidus. A single injection of lithium fails to change the striatal [Met5]enkephalin content. The increase in [Met5]enkephalin caused by chronic lithium is proportional to the serum lithium level. The extent of the increase in striatal [Met5]enkephalin content levels off at a value of about 250% that of untreated rats. This increase has a time latency of 2--3 days and reaches a plateau at 5 days. The increase that was present at 5 days was no longer evident if the treatment was continued for 2 weeks. Lithium also increases striatal [Leu5]enkephalin content by an extent equal to the increase of [Met 5]enkephalin. Based on the characteristics of the lithium-induced increase in [Met6]enkephalin content, it is proposed that lithium may reduce the rate of release of [Met5]enkephalin from the small enkephalinergic neurons that are intrinsic to the striatum; this action may be related to a change in the regulation of striatal neurons.
alpha-Bungarotoxin blocks nicotinic transmission in the avian ciliary ganglion.
Authors: Chiappinelli V A , Zigmond R E
Published: May 2006

alpha-Bungarotoxin binds to nicotinic receptors in skeletal muscle, blocking neuromuscular transmission. Because this toxin has recently been shown to bind to chicken ciliary ganglia, an attempt has been made to determine whether it also blocks nicotinic transmission in this ganglion, alpha-Bungarotoxin (1 micrometer) completely blocked nicotinic transmission in both the ciliary and choroid neurons of chicken and pigeon ciliary ganglia. The effect of the toxin could be partially reversed by prolonged washing (2--8 hr). Incubation of ganglia with d-tubocurarine (0.1 mM) prior to the addition of alpha-bungarotoxin significantly decreased the duration of the washout period necessary to restore transmission. These results suggest that d-tubocurarine and alpha-bungarotoxin are interacting with the same receptor. Under similar conditions, alpha-bungarotoxin did not block nicotinic transmission in the rat superior cervical ganglion, in agreement with previous reports. The avian ciliary ganglion is the only vertebrate autonomic ganglion in which both alpha-bungarotoxin binding and alpha-bungarotoxin blockade of transmission have been shown to occur. This ganglion therefore provides a model system for using alpha-bungarotoxin to study neuronal nicotinic receptors.
Tumor-specific transplantation antigen: use of the Ad2+ND1 hybrid virus to identify the protein responsible for simian virus 40 tumor rejection and its genetic origin.
Authors: Jay G , Jay F T , Chang C , Friedman R M , Levine A S
Published: May 2006

Cells transformed by simian virus 40 (SV40) possess a tumor-specific transplantation antigen (TSTA) that has the property of immunizing animals against syngeneic tumor challenge. We find that the early SV40 DNA segment present in the human adenovirus 2 (Ad2)-SV40 hybrid, Ad2+ND1, is sufficient to induce this SV40-specific TSTA in BALB/c mice. Moreover, studies on the intracellular distribution of TSTA activity in Ad2+ND1-infected cells, as determined by the ability of various subcellular fractions to immunize mice against syngeneic tumor challenge, have suggested a correlation between this biological activity and the presence of the SV40-specific 28,000Mr protein in coded by this hybrid virus. Both the TSTA activity and the 28,000 Mr protein are found in the plasma membrane fraction and in the perinuclear region of infected cells but are virtually undetectable in the cytoplasmic fraction. Using a hamster antitumor antiserum that can specifically immunoprecipitate the 28,000 Mr protein, we are able to demonstrate a loss of TSTA activity concomitant with the removal of this SV40-coded protein. Thus, it appears that antigenic determinants responsible for SV40-specific tumor rejection in mice are contained within the 28,000 Mr protein coded for by the early SV40 DNA segment that extends from 0.17 to 0.28 map unit.
Evaluation of the partitioning of bound inorganic phosphate during medium and intermediate phosphate in equilibrium water oxygen exchange reactions of yeast inorganic pyrophosphatase.
Authors: Hackney D D , Boyer P D
Published: May 2006

During the rapid exchange of oxygens of Pi with water catalyzed by yeast inorganic pyrophosphatase, Pi at the catalytic site may either dissociate or undergo reversible loss of an oxygen to water. The effective partitioning of bound Pi during exchange starting with medium Pi containing 18O in all four oxygens has been evaluated by mass spectral analysis of the change in the distribution of Pi species containing zero to four 18O oxygens per Pi. This analysis indicates that the rate of Pi release from the enzyme is only 1.4 times faster than the rate of reformation of the anhydrous intermediate. A similar partitioning of bound Pi is observed during PPi hydrolysis, indicating that hydrolysis and medium exchange have common intermediates. The approach should be applicable to study of related phosphate oxygen exchanges.
Guanosinetriphosphatase activity dependent on elongation factor Tu and ribosomal protein L7/L12.
Authors: Donner D , Villems R , Liljas A , Kurland C G
Published: May 2006

Incubation of electrophoretically pure samples of the Escherichia coli 50S ribosomal protein L7/L12 together with elongation factor Tu leads to the hydrolysis of GTP. Addition of elongation factor Ts stimulates this reaction. Elongation factor G cannot replace elongation factor Tu for the ribosome-free GTPase reaction dependent on L7/L12. The data suggest that elongation factor Tu and the protein L7/L12 interact directly at the ribosomal A site.
Identification of the structural proteins of an ATP-driven potassium transport system in Escherichia coli.
Authors: Laimins L A , Rhoads D B , Altendorf K , Epstein W
Published: May 2006

The three structural proteins of the ATP-driven Kdp potassium transport system of Escherichia coli [Rhoads, D. B., Waters, F. B. & Epstein, W. (1976) J. Gen. Physiol. 67, 325-341] have been identified and found to be located in the inner membrane. The high-affinity repressible Kdp system in one of four potassium transport systems in E. coli. The Kdp proteins were identified both in growing cells as well as in heavily UV-irradiated cells infected with transducing phages carrying the kdp operon. Although all previously identified ATP-driven transport systems of Gram-negative bacteria have been shown to contain a periplasmic protein component, no evidence was found for such a component or for an outer membrane component of the Kdp system. The molecular weights of the three inner membrane proteins, KdpA, KdpB, and KdpC, were determined to be 47,000, 90,000 and 22,000, respectively.
Novel template requirements of N4 virion RNA polymerase.
Authors: Falco S C , Zivin R , Rothman-Denes L B
Published: May 2006

A DNA-dependent RNA polymerase has been purified from disrupted virions of the Escherichia coli bacteriophage N4. The RNA polymerase is phage-coded and is required for class I N4 RNA synthesis, which is defined as RNA synthesized in vivo in the absence of post-infection protein synthesis. A polypeptide of molecular weight 350,000 is detected when the purified enzyme is analyzed by sodium dodecyl sulfate/polyacrylamide gel electrophoresis. N4 RNA polymerase requires denatured DNA as a template in vitro and shows a strong preference for denatured N4 DNA. With this template, transcription is asymmetric. The RNA product is complementary to only the H strand of N4 DNA. Furthermore, only class I N4 RNA is synthesized. In vivo transcription by the N4 virion RNA polymerase is inhibited by coumermycin. This result suggests that the activity of E. coli DNA gyrase, an enzyme that introduces negative supertwists into DNA, is required for N4 transcription.
Disulfide-linked high molecular weight protein associated with human cataract.
Authors: Spector A , Roy D
Published: May 2006

A major high molecular weight disulfide-linked protein has been isolated from cataractous lenses. It is only present in the water-insoluble protein fractions. This species has not been found in normal lenses of comparable age. Upon reduction of this fraction, polypeptides having molecular weights of approximately 60,000, 43,000, and 20,000 as well as a noncharacterized heterogeneous species are released. Similar sized polypeptides have been found in various noncovalently linked aggregates in both normal and cataractous lenses. Examination of the disulfide-linked protein fraction indicates that approximately 70% of the sulfhydryl groups are in the oxidized state. Although little change in the sizes of the other major polypeptides in the water-insoluble fraction is observed upon reduction, these components were also found to contain an appreciable disulfide content. Such results indicate that the only major lens fraction containing disulfide-linked polypeptide is the high molecular weight species and that the disulfides present in the remaining fractions are either intrachain disulfides or link polypeptides to small peptides.
Fluorescence probe measurement of the intralysosomal pH in living cells and the perturbation of pH by various agents.
Authors: Ohkuma S , Poole B
Published: May 2006

A quantitative method is described for the measurement of intralysosomal pH in living cells. Fluorescein isothiocyanate-labeled dextran (FD) is endocytized and accumulates in lysosomes where it remains without apparent degradation. The fluorescence spectrum of this compound changes with pH in the range 4-7 and is not seriously affected by FD concentration, ionic strength, or protein concentration. Living cells on coverslips are mounted in a spectrofluorometer cell and can be perfused with various media. The normal pH inside macrophage lysosomes seems to be 4.7-4.8, although it can drop transiently as low as 4.5. Exposure of the cells to various weak bases and to acidic potassium ionophores causes the pH to increase. The changes in pH are much more rapid than is the intralysosomal accumulation of the weak bases. Inhibitors of glycolysis (2-deoxyglucose) and of oxidative phosphorylation (cyanide or azide) added together, but not separately, cause the intralysosomal pH to increase. These results provide evidence for the existence of an active proton accumulation mechanism in the lysosomal membrane and support the theory of lysosomal accumulation of weak bases by proton trapping.
Base ratio, DNA content, and quinacrine-brightness of human chromosomes.
Authors: Korenberg J R , Engels W R
Published: May 2006

Human chromosomes were labeled with base-specific radioactive DNA precursors and examined autoradiographically to measure their DNA content and base ratio (percentage A-T base pairs). The requirement that incorporation of labeled bases be uniform during DNA synthesis was met by the use of inhibitors of de novo synthesis of DNA precursors. The genome was subdivided into 75 segments based on quinacrine banding, and the base ratio of each was calculated by a method that corrects for bias due to the scatter of grains about their source. Estimates of base ratio are shown to be sufficiently precise to detect variability among chromosomes and among segments within a chromosome. Analysis of these data and of measurements of the quinacrine fluorescence intensity of segments leads to the following conclusions. Base ratio is positively correlated with brightness, as predicted from independent in vitro studies. Larger chromosomes tend to have higher base ratios and to be brighter than smaller ones. The best prediction of the brightness of a segment must take into account not only its base ratio but also its DNA content. To explain these results, we suggest an evolutionary model in which chromosomes containing repeated sequences of A-T-rich DNA tend to grow by means of unequal sister chromatid and meiotic exchanges.
Growth hormone modulation of murine erythroleukemia cell growth in vitro.
Authors: Golde D W , Bersch N , Li C H
Published: May 2006

There are few studies showing a biological effect of growth hormone (somatotropin) on cell proliferation in vitro at physiological concentrations. We report here that Friend virus-infected erythroleukemia cells are responsive to growth hormone in vitro. Using a serum-free clonogenic assay we found as little as 0.1 ng of human growth hormone per ml caused a prominent stimulation of cell proliferation. Peak activity of human growth hormone occurred at 200 ng/ml, resulting in a 2-fold increase in cloning. Human chorionic somatomammotropin and the Cys(Cam)53-hGH(1-134) fragment of human growth hormone were also active, but a biologically inert oxidized human growth hormone had no growth-promoting effect in vitro. Cell proliferation was stimulated by insulin with peak potentiation occurring at 1 ng/ml, and prolactin had a demonstrable stimulatory effect between 50 and 100 ng/ml. These observations indicate that growth hormone and related polypeptides have a direct effect on the in vitro proliferation of erythroleukemia cells in the absence of serum. The results confirm a direct action of growth hormone on mammalian cells and suggest that pituitary hormones may affect leukemic cell growth.
Nerve growth factor-induced fiber outgrowth from isolated rat adrenal chromaffin cells: impairment by glucocorticoids.
Authors: Unsicker K , Krisch B , Otten U , Thoenen H
Published: May 2006

Addition of nerve growth factor to cultures of dissociated rat adrenal medullary cells caused fiber outgrowth from chromaffin cells. These fibers exhibited all the characteristics of neurites, particularly the formation of typical growth cones exhibiting intense catecholamine-specific fluorescence. Because this nerve growth factor-mediated neurite outgrowth could be abolished by physiological concentrations of glucocorticoids, it is concluded that the high glucocorticoid concentrations normally present in the adrenal medulla prevent the fiber outgrowth from medullary chromaffin cells in vivo. In dissociated sympathetic neurons the same concentrations of glucocorticoids markedly reduce but do not completely abolish neuronal fiber outgrowth.
In vitro
release of [5-methionine]enkephalin and [5-leucine]-enkephalin from the rat globus pallidus
Authors: Bayon Alejandro , Rossier Jean , Mauss Alice , Bloom Floyd E. , Iversen Leslie L. , Ling Nicholas , Guillemin Roger
Published: May 2006

Endogenous [5-methionine]enkephalin (Metenkephalin) and [5-leucine]enkephalin (Leu-enkephalin) are released from perfused slices of rat globus pallidus by increased K
+
in a Ca
2+
-dependent manner. Tissue perfused for 40 min contained only 26% of the Met-enkephalin and 44% of the Leu-enkephalin found in the freshly dissected tissue. After perfusion, the mean (±SEM) ratio (wt/wt) of Met-enkephalin to Leu-enkephalin was 3.4 ± 0.2 compared with 5.8 ± 0.2 in the fresh tissue. The degradation of trace amounts of synthetic [
3
H]enkephalins in the perfusing medium during stimulated release seems to reflect the accelerated degradation of enkephalin released from the tissue: 63% of the Met-enkephalin and 23% of the Leu-enkephalin were degraded in a medium containing bacitracin (30 μg/ml). The mean ratio (wt/wt) of the Met-enkephalin to the Leu-enkephalin recovered after release by exposure of slices to 50 mM K
+
was 2.7 ± 0.3. When perfusates were corrected for degradation, this ratio increased to about 5.5 which is higher than that found in the perfused tissue. The differences in release, tissue loss, and catabolism of the two enkephalins may be reflecting differences in the metabolic systems operating on the pentapeptides, but this interpretation will have to be validated by
in vivo
release experiments. In any event these observations strongly suggest that both enkephalins can be considered candidate neurotransmitters in the rat globus pallidus.
Evidence for existence of a yearly clock in surgically and self-blinded chipmunks.
Authors: Richter C P
Published: May 2006

By use of simplified technique and constant environmental conditions, I have demonstrated the existence in the chipmunk of a yearly clock. In a blinded chipmunk the clock manifested itself by remarkably consistent changes in running activity, food and water intake, and body weight over 6 1/2 yr. Studies on freshly trapped chipmunks kept in the same laboratory environment but with alternating light and darkness (12 hr each), showed that, when their eyes were covered for much of the light period, they reduced their exposure to light to preserve the activity of the yearly clock. Laboratory-adapted chipmunks that do not shield their eyes from light do not show the clock. The yearly clock has all the characteristics of the 24-hr clock, including sharply defined active and inactive phases, and must likewise play an important part in the animal's survival. Light would appear to be the chief or only cue for the clock. The period lengths did not change with age during the 6 1/2 yr.
Lysyl-derived aldehydes in outer membrane proteins of Escherichia coli.
Authors: Diedrich D L , Schnaitman C A
Published: May 2006

The major outer membrane proteins from Escherichia coli K-12 are modified to contain alpha-aminoadipic acid delta-semialdehyde (allysine). The allysine was found to be derived from lysine and it was identified by derivatizing it to chloronorleucine by reduction, alpha-aminoadipic acid by oxidation, and to alpha,epsilon-diaminopimelic acid by reacting it with CN- and NH3. The alpha-aminoadipic acid was identified by mass spectrometry. Two major outer membrane proteins were found to possess allysine, a modified lysine characteristically found to connective tissue.
A bacterial clone synthesizing proinsulin.
Authors: Villa-Komaroff L , Efstratiadis A , Broome S , Lomedico P , Tizard R , Naber S P , Chick W L , Gilbert W
Published: May 2006

We have cloned double-stranded cDNA copies of a rat preproinsulin messenger RNA in Escherichia coli chi1776, using the unique Pst endonuclease site of plasmid pBR322 that lies in the region encoding amino acids 181-182 of penicillinase. This site was reconstructed by inserting the cDNA with an oligo(dG)-oligo(dC) joining procedure. One of the clones expresses a fused protein bearing both insulin and penicillinase antigenic determinants. The DNA sequence of this plasmid shows that the insulin region is read in phase; a stretch of six glycine residues connects the alanine at position 182 of penicillinase to the fourth amino acid, glutamine, of rat proinsulin.
Changes in membrane potential of human granulocytes antecede the metabolic responses to surface stimulation
Authors: Korchak H. M. , Weissmann Gerald
Published: May 2006

Human granulocytes (polymorphonuclear leukocytes) exposed to surface stimuli [e.g., immune complexes, concanavalin A (Con A)] generate O
2
·
-
, undergo a respiratory burst, and secrete lysosomal enzymes. To study the earliest reaction of ligands with surface receptors of granulocytes, purified cells were exposed to bovine serum albumin-anti-albumin complexes (Fc receptors) or Con A (glycoprotein receptors). The membrane potential (ΔΨ) was measured by distribution of the lipophilic cation [
3
H]triphenylmethyl phosphonium ion. The Nernst equation yielded a resting ΔΨ of -26.7 mV. Beginning within 10 sec after exposure to the antigen-antibody complex or to Con A, the cells responded with a rapid hyperpolarization → depolarization → slow hyperpolarization. Even when phagocytosis was inhibited by cytochalasin B, the triphasic response was obtained: evidence for
surface
interaction. The hyperpolarization response anteceded O
2
·
-
generation (continuous recording) by at least 20-30 sec. O
2
·
-
generation in response to immune complexes was stimulated by Ca
2+
whereas ΔΨ remained unchanged; lack of Ca
2+
in the medium did not inhibit the ΔΨ response. Dissociation of membrane hyperpolarization from subsequent metabolic responses (O
2
·
-
generation) was also found in the presence of steroids (hydrocortisone, methylprednisolone), which inhibited O
2
·
-
generation but did
not
inhibit the ΔΨ response to antigen-antibody complex. Because O
2
·
-
generation could be stimulated (Ca
2+
) or depressed (steroids) without affecting ΔΨ, the data suggest that ΔΨ is involved in primary triggering of phagocytic cells and that metabolic stimulation is a secondary consequence of ligand-receptor interactions.
Membrane sialic acid on target particles modulates their phagocytosis by a trypsin-sensitive mechanism on human monocytes.
Authors: Czop J K , Fearon D T , Austen K F
Published: May 2006

Monolayers of human peripheral blood monocytes in the absence of exogenous proteins ingest a variety of natural particulate activators of the human alternative complement pathway. Sheep erythrocytes, which do not ordinarily activate the human alternative complement pathway or initiate a direct monocyte phagocytic response, can be modified to exhibit both functions by the deletion or alteration of membrane sialic acid residues. Enzymatic removal of the sialic acid residues with sialidase or their conversion to heptulosonic acid derivatives by limited oxidation with NaIO4 and reduction with BH4- have equivalent dose-response effects on the capacity of the altered sheep erythrocytes to initiate the phagocytic response by human monocytes or to activate the alternative pathway in human serum. The deposition of C3b on native sheep erythrocytes had little effect on their ingestion by human monocytes, whereas the fixation of C3b on desialated sheep erythrocytes had a synergistic effect on the percentage of monocytes ingesting such a particle. The monocyte receptor essential for ingestion of desialated sheep erythrocytes or desialated sheep erythrocytes bearing C3b was inactivated by concentrations of trypsin that also prevented the monocytes from ingesting natural activators of the human alternative complement pathway, but did not alter the receptors for C3b or the Fc portion of IgG. The capacity of the nonimmune host to respond to desialated particles by initiating the monocyte ingestive process and by activating the alternative complement pathway to provide the synergy afforded by C3b deposition on that particle represents a primitive biochemical basis for differentiation of nonself from self.
Origin and direction of replication in mitochondrial DNA molecules from Drosophila melanogaster.
Authors: Goddard J M , Wolstenholme D R
Published: May 2006

From a consideration of the various structural forms of partially replicated mitochondrial DNA (mtDNA) molecules from Drosophila melanogaster embryos observed in the electron microscope, it appears that the majority of molecules are replicated by a highly asymmetrical mode in which synthesis on one strand is up to 99% complete before synthesis on the second strand is initiated. Replication of the minority of molecules involves a more nearly symmetrical synthesis of the two complementary strands. The D. melanogaster mtDNA molecules have physical features with respect to which the origin and direction of replication could be mapped. These features are (i) a single region accounting for approximately 25% of the circular contour length and rich in adenine + thymine, and (ii) four EcoRI sites, all of which lie outside of this region. Molecules of this mtDNA were subjected to partial denaturation, EcoRI digestion, or partial denaturation after EcoRI digestion and the products were examined in the electron microscope. Complex forms interpretable as originating from replicative intermediates were observed. The size and structure of the components of these complex forms were wholly consistent with the interpretation that, in all of these mtDNA molecules, replication originates at, or close to, the center of the adenine + thymine-rich region and proceeds unidirectionally around the molecule toward the EcoRI site lying closest to the adenine + thymine-rich region.
Alterations of hepatic Na
+
,K
+
-ATPase and bile flow by estrogen: Effects on liver surface membrane lipid structure and function
Authors: Davis Roger A. , Kern Fred , Showalter Radene , Sutherland Eileen , Sinensky Michael , Simon Francis R.
Published: May 2006

Administration of the synthetic estrogen ethinyl estradiol (17α-ethinyl-1,3,5-estratriene-3,17β-diol) decreases hepatic Na
+
,K
+
-ATPase (ATP phosphohydrolase; EC 3.6.1.3) activity and bile flow to 50% and alters the composition and structure of surface membrane lipid in rats. Although the content of phospholipids was not changed by treatment, free cholesterol (130%) and cholesterol esters (400%) were increased in liver surface membrane fractions. These observations correlate with changes in membrane viscosity, as shown by electron spin resonance probes. Both rotational correlation time, using the isotropic probe methyl (12-nitroxyl)stearate, and the order parameter, determined by the anisotropic probe 5-nitroxylstearic acid, were significantly increased in liver surface membrane fractions from rats treated with ethinyl estradiol. Administration of Triton WR-1339, a nonionic detergent that corrects hepatic and serum lipid changes caused by ethinyl estradiol treatment, restored toward normal elevated membrane lipids and viscosity as well as Na
+
,K
+
-ATPase activity and bile flow. Although restoration of normal liver surface membrane structure and function may be due to reversal of abnormal lipid composition, detergents also may directly alter membrane enzyme activity. Addition of Triton WR-1339
in vitro
increased Na
+
,K
+
-ATPase activity and reduced membrane viscosity of surface membranes from rats treated with ethinyl estradiol. Triton had no effect on either parameter in normal membrane preparations. Studies of membrane structure and function both
in vivo
and
in vitro
suggest that alterations in lipid composition may alter Na
+
,K
+
-ATPase function and bile flow.
Simplified method for purification of ribonuclease H from calf thymus.
Authors: Stavrianopoulos J G , Chargaff E
Published: May 2006

An improved purification procedure for the isolation of ribonuclease H(hybrid nuclease; RNA-DNA-hybrid ribonucleotidohydrolase, EC 3.1.4.34) from the thymus of 4-to 6-months-old calves yields two highly active forms of the enzyme, designated as ribonuclease H1 and H2. Their isoelectric points are 5.0 +/- 0.05 and 5.25 +/- 0.05, respectively; their molecular weight, estimated from gel filtration, is in both cases 64,000 +/- 2000. On sodium dodecyl sulfate gel electrophoresis, two principal bands were identified, with molecular weights of 32,000 and 21,000. The nature of the nucleotides at the 3'-OH terminals, produced initially by the enzymic hydrolysis of hybridized RNA, was examined and shown to be a function of the divalent metal ion employed as activator.
Functional
lac
carrier protein in cytoplasmic membrane vesicles isolated from
Escherichia coli:
Temperature and pH dependence of dansyl-galactoside binding
Authors: Therisod Hélène , Weil Rudolf , Shechter Emanuel
Published: May 2006

6′-(
N
-Dansyl)aminohexyl-1-thio-β-D-galactopyranoside binds specifically to the
lac
carrier protein in cytoplasmic membrane vesicles isolated from
Escherichia coli
. Binding can be induced by substrate oxidation (generation of an electrochemical gradient of protons), by potassium efflux in the presence of valinomycin (generation of a potassium diffusion potential), and by passive, carrier-mediated lactose efflux. We show that in all three cases the number of binding sites is temperature dependent. Binding is maximal and constant above 20°; it decreases between 20° and 10°. Oxidation of substrate (D-lactate) leads to the development of an electrochemical gradient of protons across the membrane (interior negative and alkaline), which is composed of interconvertible electrical and chemical gradients. We show that both the electrical potential across the membrane and the chemical difference in proton concentrations across the membrane are independent of temperature between 5° and 25°. We show that the number of binding sites induced by D-lactate oxidation depends on pH. At both 25° and 5°, the number of binding sites increases from pH 5 to pH 6.5, remains constant between pH 6.5 and 7, and decreases from pH 7 to pH 8. In contrast, the number of binding sites induced by passive, carrier-mediated lactose efflux is independent of pH between pH 5.5 and pH 8.

From these findings, we conclude that the pH- and temperature-dependent effects on the number of 6′-(
N
-dansyl)aminohexyl-1-β-thio-D-galactopyranoside binding sites have different origins. The pH dependence of binding is energy linked and reflects in part the pH dependence of the electrochemical gradient of protons across the membrane generated by substrate oxidation. The temperature dependence is not an energy-linked phenomenon. The decrease of the number of binding sites at low temperature probably reflects the aggregation of the
lac
carrier protein with other membrane proteins. This aggregation takes place as a consequence of the conformational disorder-to-order transition of the membrane lipids and the concomitant preferential segregation of the
lac
carrier protein in the membrane domains containing the disordered lipids.
Rhynchosporoside, a host-selective toxin produced by
Rhynchosporium secalis
, the causal agent of scald disease of barley
Authors: Auriol Pierre , Strobel Gary , Beltran J. Pio , Gray Gary
Published: May 2006

Rhynchosporoside, a phytotoxic compound, has been isolated from cultures of
Rhynchosporium secalis
, the causal agent of scald disease of barley. The toxin is a cello-bioside of 1,2-propanediol. The compound may play some role in symptom expression because it was isolated from diseased plants in concentrations similar to those that could cause symptoms in toxin-treated plants. The toxin causes leaf tip and marginal necrosis and subsequent chlorosis of the entire leaf. The toxin affects only certain cultivars and lines of barley and rye; however, it also affects certain nonhosts of
R. secalis
. The genetic factor controlling host resistance to the fungus is not identical to that controlling insensitivity to the toxin.
Mutants of Escherichia coli altered in both genes coding for the elongation factor Tu.
Authors: Van de Klundert J A , Van der Meide P H , Van de Putte P , Bosch L
Published: May 2006

Genetic analysis of a mutant of Escherichia coli resistant to the antibiotic mocimycin is presented. This resistance is due to alterations in both tuf genes coding for the elongation factor Tu. Mocimycin resistance is recessive. Bacteria carryong only one tuf gene from the resistant mutant are still mocimycin sensitive. If the mutant gene is the tufA gene, the seisitive cells can be made resistant through inactivation of the tufB gene by insertion of the bacteriophage milliunits genome. Conditional mocimycin-resistant mutants ban also be isolated when the tufB gene is altered by an amber or a temperature-sensitive mutation. When only the tufB allele from the original mocimycin-resistant mutant is present, inactivation of the wild-type tufA gene fails to give viable mocimycin-resistant progeny. We conclude that the tufA mutant allele codes for a functional mocimycin-resistant EF-Tu, whereas the mutant tufB gene does not code for a functional product.
Selective association of murine T lymphoblastoid cell surface alloantigens with Mycoplasma hyorhinis.
Authors: Wise K S , Cassell G H , Action R T
Published: May 2006

Mycoplasma hyorhinis, isolated by isopycnic centrifugation from supernatants of a persistently infected murine T lymphoblastoid cell line, demonstrated the presence of the Thy-1.1 differentiation alloantigen and H-2Kk histocompatibility antigens. The murine leukemia virus-related gp70 antigen also present on the surface of these lymphoblastoid cells was absent from mycoplasma preparations. Quantitative assessment of Thy-1.1 present in preparations of M. hyorhinis revealed a specific activity greater or equal to that of membrane preparations from lymphoblastoid cells, suggesting a marked accumulation of this T lymphoblastoid cells, suggesting a marked accumulation of this T lymphocyte antigen by membrane-associated mycoplasmas. The accumulation of the Thy-1.1 antigen in association with purified mycoplasmas was also demonstrated in lymphoblastoid cells experimentally infected with a defined culture of M. hyorhinis.
Volatile anesthetic facilitation of
in vitro
desensitization of membrane-bound acetylcholine receptor from
Torpedo californica
Authors: Young A. P. , Brown F. F. , Halsey M. J. , Sigman D. S.
Published: May 2006

Incubation of membrane fragments bearing acetylcholine receptors from
Torpedo californica
under an atmosphere of 3% halothane, 1% chloroform, or 6% diethyl ether greatly facilitates the carbamoylcholine-induced structural transition of the acetylcholine receptor reflected by alterations in the rate of binding of
125
I-labeled α-bungarotoxin. The half-time of this ligand-induced conformational change is decreased to 10% of the original value after incubation of the membranes with these volatile anesthetics at or near their clinical concentrations. The synergistic effects observed with the general anesthetics and carbamoylcholine are abolished if the membranes are incubated under a stream of air after exposure to the inhalational agents. The antagonist
d
-tubocurarine exerts a smaller yet measurable time-dependent effect on the toxin-binding properties of the membrane fragments. Treatment of membranes with general anesthetics facilitates this antagonist-induced conversion of the receptor protein as well. The synergism between ligands and general anesthetics may be due to the disruption by these inhalational agents of interactions at the protein-lipid interface, which may play a significant role in determination of receptor conformation. In addition, if the conformational change induced by carbamoylcholine observed in the snake toxin binding assay corresponds to desensitization of the receptor
in vivo
, facilitation of this conformational change by volatile anesthetics provides an attractive model for the pharmacological action of these compounds.
DNA binding activity from cultured human fibrolasts that is specific for partially depurinated DNA and that inserts purines into apurinic sites.
Authors: Deutsch W A , Linn S
Published: May 2006

A protein of molecular weight approximately 120,000 was isolated from cultured human fibroblasts and HeLa cells on the basis of its ability to bind specifically to apurinic DNA. After separation from apurinic endonuclease activity, the protein was found to incorporate purine, but not pyrimidine, bases specifically into depurinated DNA so as to protect the apurinic sites from alkali. Purine base insertion activity was sensitive to heating and freezing as well as to caffeine and EDTA; it required K+ but not a divalent cation. Guanine, but not adenine, was incorporated into depurinated poly(dG-dC), whereas adenine, but not guanine, was incorporated into poly(dA-dT). After incorporation into depurinated DNA, guanine could be reisolated as dGMP. Although this activity suggests an alternative pathway for DNA repair that is independent of nucleotide excision, other functions for such an enzyme are possible.
Definition of cytochrome
c
binding domains by chemical modification: Kinetics of reaction with beef mitochondrial reductase and functional organization of the respiratory chain
Authors: Speck Samuel H. , Ferguson-Miller Shelagh , Osheroff Neil , Margoliash E.
Published: May 2006

An assay has been developed to study the steady-state kinetics of the reduction of cytochrome
c
by purified beef heart mitochondrial cytochrome
c
reductase (cytochrome
bc
1
complex, complex III). An analogue of coenzyme Q
2
(2,3-dimethoxy-5-methyl-6-decylhydroquinone) was employed as an antimycin-sensitive reductant. The kinetics of reaction of ten different mono(4-carboxy-2,6-dinitrophenyl) derivatives of horse cytochrome
c
were determined. The modified proteins showed higher apparent
K
m
values than the native protein and greater sensitivity to ionic strength, defining an interaction domain on cytochrome
c
for purified cytochrome
c
reductase. This interaction site is located on the front surface of the molecule (which contains the exposed heme edge) and surrounds the point at which the positive end of the dipole axis crosses the surface of the protein. The site is similar to that previously determined for mitochondrial cytochrome
c
oxidase and yeast cytochrome
c
peroxidase, suggesting that the primary interaction with redox partners is directed by the dipolar charge distribution on cytochrome
c
. The extensive overlapping of the interaction domains for the mitochondrial cytochrome
c
oxidase and reductase indicates that cytochrome
c
must be mobile in order to transfer electrons between them, depending on their relative positions in the membrane. Whether such mobility is necessary in intact mitochondria depends on whether the interactions with the complete membrane-bound system are the same as with the purified components.