bluuebunny/crossref_metadata_2025 huggingface dataset:
Carbon-13 nuclear magnetic resonance study of chondroitin 4-sulfate in the proteoglycan of bovine nasal cartilage.
Authors: Brewer C F , Keiser H
Published: May 2006

The Fourier transform 13C nuclear magnetic resonance spectra of bovine nasal cartilage proteoglycan subunit and complex and whole bovine nasal cartilage were obtained and compared with that of chondroitin 4-sulfate. The spectrum of chondroitin 4-sulfate in solution revealed multiple resolvable resonances with linewidths that are consistent with considerable segmental motion in the polysaccharide chain. The spectra of proteoglycan subunit and complex in solution and that of whole cartilage were very similar to that of free chondroitin 4-sulfate chains. This indicates that the linkage of multiple chondroitin sulfate chains to proteoglycan core protein and the association of proteoglycan with collagen and other constituents of cartilage matrix does not significantly alter the structure and motions of these chains.
Kinetics of action of pepsin on fluorescent peptide substrates.
Authors: Sachdev G P , Fruton J S
Published: May 2006

Oligopeptide substrates of porcine pepsin (E) of the type A-Phe-Phe-B (S) that are cleaved solely at the Phe-Phe bond under the conditions of these studies, and bearing an amino-terminal fluorescent probe group (mansyl or dansyl), have been used for stopped-flow measurements of the rate of formation of the A-Phe product. These experiments were conducted under conditions of [E] greater than [S], and the kinetic data were compared with those obtained under conditions of [S] greater than [E] for the formation of the Phe-B product (the same in all cases). The results for substrates with A = mansyl-Gly, mansyl-Gly-Gly, and dansyl-Gly-Gly support the conclusion that the rate-limiting step in the over-all catalytic process is associated with the scission of the Phe-Phe bond in the first detectables ES complex. Although the rate of this step varies widely with the nature of the A portion of A-Phe-Phe-B, the magnitude of the dissociation constant of ES is relatively invariant. This supports the view that, in the cleavage of oligopeptide substrates by pepsin, secondary enzyme--substrate interactions may cause conformational changes at the catalytic site, and that a portion of the total binding energy may be used for the attainment of the transition state in the bond-breaking step. With substrates that are hydrolyzed extremely rapidly (A = dansyl-Gly-Ala, dansyl-Ala-Ala), the rate of formation of the A-Phe product appears to be faster than the steady-state rate, suggesting that an additional step has become kinetically significant in the over-all process. This step may be associated with the return of the conformation of the active site to its original state.
Isolation of subunits of citrate lyase and characterization of their function in the enzyme complex.
Authors: Dimroth P , Eggerer H
Published: May 2006

Citrate lyase [EC 4.1.3.6; citrate oxaloacetate-lyase (pro-3S-CH2-COO--leads to acetate)] from Klebsiella aerogenes has been dissociated with urea; the three different subunits, alpha-chain (molecular weight congruent to 54,000), beta-chain (molecular weight congruent to 32,000), and gamma-chain (acyl carrier protein; molecular weight congruent to 10,000), have been isolated in pure and catalytically active state. Recombination of the three subunits produced citrate lyase that was indistinguishable from the untreated enzyme. The alpha-chain in the presence of acetyl-S-acyl carrier protein catalyzed the formation of the corresponding citryl thioester with liberation of acetate, and the beta-chain catalyzed the cleavage of citryl-S-acyl carrier protein with liberation of oxaloacetate. A simple enzymic method for the preparation of citryl-S-acyl carrier protein is described.
The glass point of elastin.
Authors: Kakivaya S R , Hoeve C A
Published: May 2006

Elastin undergoes a glass transition in a temperature range depends on its water content. This behavior is similar to that of amorphous polymers swollen with solvent and, therefore, is additional evidence for the random network model proposed for the structure of elastin.
Hemoglobin Cranston, an unstable variant having an elongated beta chain due to nonhomologous crossover between two normal beta chain genes.
Authors: Bunn H F , Schmidt G J , Haney D N , Dluhy R G
Published: May 2006

An asymptomatic woman was found to have a compensated hemolytic state due to an unstable hemoglobin variant, comprising 35% of the total. Peptide maps of tryptic digests of the abnormal beta chain were identical to those of beta A except that tryptic peptide 15 (Tyr-His-COOH) was absent and a new peptide was detected, containing equivalent amounts of Ser, Ile, Thr, and Lys. Its sequence was determined by manual Edman degradation. An additional hydrophobic peptide isolated by counter-current distribution contained: Asx, Ser, Ala, Tyr, 2 Phe, and 3 Leu. Its sequence was determined on an automatic solid phase sequencer. Digestion with carboxypeptidase A confirmed the C-terminal sequence. Hemoglobin Cranston has an elongated beta chain with the following structure: (see article). This variant is the first "adult" human hemoglobin known to contain isoleucine. It is likely that hemoglobin Cranston arose because of a nonhomologous crossover of two normal beta chain genes, probably during meiosis, with the insertion of two nucleotides (AG) at position 144, resulting in a frame shift. Hemoglobin Cranston provides new information on the structure of the beta chain gene as well as an explanation of both the structure and genetic basis of hemoglobin Tak, the only other elongated beta chain variant that has been described.
Control of meal size by central noradrenergic action.
Authors: Ritter R C , Epstein A N
Published: May 2006

Previous investigations of central noradrenergic effects on food intake have concentrated on the use of high doses of noradrenaline (two to 200 times brain noradrenaline content). In this work we examined the effect of low doses of noradrenaline (not exceeding brain noradrenaline content) on the parameters of spontaneous ingestive behavior. By arranging for rats to trigger remote infusions of noradrenaline into their own anterior forebrains at the beginning of spontaneously initiated meals, meal size was very reliably increased more than 200% by doses of 0.015--0.37 nmol (2.5--62 ng of noradrenaline base) (n = 12). The effect was alpha-adrenergic. It was blocked by phentolamine but not by propranolol. Infusions of noradrenaline at the above doses, which nearly triple meal size, did not elicit eating when made during an intermeal interval, nor did they influence the length of the intermeal interval when made 60 min after the termination of an uninfused meal. These results show that noradrenaline increased food intake at doses less than 1% of the brain's endogenous noradrenaline content. Meal size is more susceptible to alteration by noradrenaline manipulations than is meal frequency. The brain's own noradrenergic system may function to sustain food intake once feeding is initiated. This function of brain noradrenaline may control spontaneous meal size.
Characterization of residual enzyme activity in fibroblasts from patients with adenosine deaminase deficiency and combined immunodeficiency: evidence for a mutant enzyme.
Authors: Hirschhorn R , Beratis N , Rosen F S
Published: May 2006

A proportion of patients suffering from the autosomal recessive form of severe combined immunodeficiency have an inherited deficiency of adenosine deaminase (EC 3.5.4.4; adenosine aminohydrolase) (erythrocyte isoenzyme). We have, however, found residual adenosine deaminase activity in fibroblasts derived from four such patients. The enzyme responsible for this activity is biochemically homologous with the high-molecular-weight tissue isoenzyme of adenosine deaminase found in normal fibroblasts and tissues other than erythrocytes. The residual adenosine deaminase has an altered electrophoretic mobility, increased heat stability as compared to normals, and can be detected in fibroblasts of obligate heterozygotes. Our previous studies have indicated that the tissue and erythrocyte adenosine deaminase isoenzymes contain a common catalytic unit controlled by the gene affected in severe combined immunodeficiency with absent adenosine deaminase (erythrocyte isoenzyme). This residual adenosine deaminase therefore represents, most likely, a "mutant" enzyme in fibroblasts of patients with severe combined immunodeficiency. The data support the hypothesis that, in these patients, severe combined immunodeficiency is due to a mutation at the adenosine deaminase locus.
Chromatographic isolation of the hemagglutinin polypeptides from influenza virus vaccine and determination of their amino-terminal sequences.
Authors: Bucher D J , Li S S , Kehoe J M , Kilbourne E D
Published: May 2006

The influenza virus hemagglutinin polypeptides, HA1 and HA2, have been purified by gel filtration in the presence of sodium dodecyl sulfate from a vaccine preparation of the recombinant strain Heq1N2. Use of this technique for purification of the hemagglutinin polypeptides eliminated the need for proteolytic agents for removal of the hemagglutinin from the virus particles and 100-300 mg of virus yielded 10-30 mg of viral protein per chromatographic cycle. Because proteolysis is not required to remove the spikes from the viral envelope, the envelope-embedded HA2 polypeptide was purified in its entirety for structural analysis. Amino-terminal sequence analysis of the smaller polypeptide, HA2, revealed a cyclic repetition of glycyl residues through the first 24 residues at every third to fourth position. The sequence through the first 10 residues was identical to that presented by Skehel and Waterfield for other type A influenza viruses [(1975) Proc. Nat. Acad. Sci. USA 72, 93-97]. The HA1 (Heq/) polypeptide, on the other hand, had different amino acids at three or four out of the first 10 residues of the amino-terminal sequence when compared to HA1 from H0, H1, or H2 subtypes (Skehel and Waterfield). The present study has demonstrated the feasibility of the use of vaccine virus as a source of large quantities of viral protein for determination of primary structure.
Polypeptide chain initiation in eukaryotes: initiation factor requirements for translation of natural messengers.
Authors: Filipowicz W , Sierra J M , Nombela C , Ochoa S , Merrick W C , Anderson W F
Published: May 2006

A protein-synthesizing system consisting of ribosomes and supernatant of undeveloped Artemia saline embryos is used for assay of mRNA translation and initiation factors. This system contains the components needed for chain elongation but has low levels of mRNA and initiation factors. Exogenous mRNA is readily translated upon addition of high-speed supernatant or ribosomal salt wash of developing embryos as a source of initiation factors (IF). This requirement can be largely satisfied by a mixture of the reticulocyte factors IF-MP, IF-M3, IF-M2A, and IF-M2B. A. salina IF-M1, which is present in undeveloped embryo supernatant, can be inactivated by A. salina IF-M1 antibody without affecting translation.
A DNA fragment from the origin of single-strand to double-strand DNA replication of bacteriophage fd.
Authors: Schaller H , Uhlmann A , Geider K
Published: May 2006

A specific complex is formed between fd DNA, Escherichia coli DNA unwinding protein, and RNA polymerase (EC 2.7.7.6; nucleosidetriphosphate:RNA nucleotidyltransferase) during the first steps in the conversion of the single-stranded viral DNA to the double-stranded replicative form. In this complex a unique DNA fragment of about 120 nucleotides is protected against nuclease digestion. Both the requirements for its isolation and its position on the map of the phage genome indicate that the fragment contains the origin of single-strand to double-strand DNA replication. The isolated DNA fragment possesses double-strand-like characteristics, which protect it from being covered by the DNA unwinding protein and thus indirectly positions the RNA polymerase to the origin of replication.
Chemical and enzymatic synthesis of lactose operator of Escherichia coli and its binding to lactose repressor.
Authors: Bahl C P , Wu R , Itakura K , Katagiri N , Narang S A
Published: May 2006

The 21-nucleotide-long duplex DNA constituting the lactose operator sequence of E. coli has been synthesized by both chemical and enzymatic methods. The synthetic duplex has the essential feature of the lactose operator as seen by its binding to the lactose repressor. The binding of the synthetic operator fragment to the lactose repressor is specific because it is inhibited by the inducing ligand isopropyl-beta-D-thiogalactoside. Thus, it is now possible to show that a chemically synthesized oligodeoxynucleotide can be specifically recognized by its natural regulatory protein.
Human somatotropin: biological characterization of the recombinant molecule.
Authors: Li C H , Hayashida T , Doneen B A , Rao A J
Published: May 2006

The recombinant hormone obtained by non-covalent interaction of the NH2-terminal 134 amino acid fragment with the COOH-terminal 51 amino acid fragment of the reduced-carbamidomethylated human somatotropin molecule is found to exhibit nearly full biological activity of the native hormone, as evidenced by the stimulation of hepatic ornithine decarboxylase (L-ornithine carboxy-lyase, EC 4.1.1.17) in vivo and protein synthesis in mouse mammary gland in vitro. Radioimmunoassay data indicate that the recombinant behaves immunochemically in a manner almost identical to that of the native hormone.
Mapping of in vivo messenger RNAs for bacteriophage phiX-174.
Authors: Hayashi M , Fujimura F K , Hayashi M
Published: May 2006

In vivo messenger RNA for bacteriophage phiX174 was fractionated in agarose gels into a number of discrete species ranging in size from 0.23 X 10(6) to 2.3 X 10(6) daltons. These RNA species were eluted from the gels and hybridized to specific fragments derived from phiX-174 replicative form DNA by cleavage with restriction enzymes. A map of the orientation of in vivo messenger RNAs with respect to the bacteriophage genetic map was constructed. This map indicated that initiation of messenger RNA occurred before gene B, gene C or D, and probably before gene A and that termination occurred after genes E, F, G, and H. Termination of transcription at any particular site appeared not to be entirely effective such that a number of overlapping transcripts with the same 5'-terminus was observed. Messenger RNA for gene A seemed to be relatively unstable.
Evidence for somatic rearrangement of immunoglobulin genes coding for variable and constant regions.
Authors: Hozumi N , Tonegawa S
Published: May 2006

A high-molecular-weight DNA from Balb/c mouse early embryo or from MOPC 321 plasmacytoma (a k-chain producer) was digested to completion with Bacillus amyloliquefaciens strain H restriction enzyme (BamH I). The resulting DNA fragments were fractionated according to size in preparative agarose gel electrophoresis. DNA fragments carrying gene sequences coding for the variable or constant region of k chains were detected by hybridization with purified, 125I-labeled, whole MOPC 321 K MRNA and with its 3'-end half. The pattern of hybridization was completely different in the genomes of embryo cells and of the plasmacytoma. The pattern of embryo DNA showed two components, one of which (molecular weight=6.0 million) hybridized with C-gene sequences and the other (molecular weight=3.9 million) with V-gene sequences. The pattern of the tumor DNA showed a single component that hybridized with both V-gene and C-gene sequences and that is smaller (molecular weight=2.4 million) than either of the components in embryo DNA. The results were interpreted to mean that the Vk and Ck genes, which are some distance away from each other in the embryo cells, are joined to form a contiguous polynucleotide stretch during differentiation of lymphocytes. Such joining occurs in both of the homologous chromosomes. Relevance of these findings with respect to models for V-C gene joining, activation of a specific V k gene, and allelic exclusion in immunoglobulin gene loci is discussed.
Vitamin A-containing lipocytes and formation of type III collagen in liver injury.
Authors: Kent G , Gay S , Inouye T , Bahu R , Minick O T , Popper H
Published: May 2006

Hepatocellular necrosis in carbon tetracholride-induced injury of rats is associated with an accumulation of lipocytes (perisinusoidal cells or Ito cells) containing fat droplets and giving vitamin A fluorescence. In the subsequent formation of connective tissue septa, transitional cells having morphologic characteristics of lipocytes and fibroblasts are abundant and are associated with the appearance of type III collage-. The features suggest that the lipocyte is the precursor of the fibroblasts responsible for parenchymal fibrillogenesis and under these conditions forms type III collagen. The process is a postulated link between hepatocellular necrosis and fibrosis.
Aryl 4-monooxygenase and cytochrome P-450 in the aorta: possible role in atherosclerosis.
Authors: Juchau M R , Bond J A , Benditt E P
Published: May 2006

Aryl 4-monooxygenase [aniline, reduced-flavoprotein:oxygen oxidoreductase (4-hydroxylating); EC 1.14.14.1] activity was searched for and found in homogenates of aorta walls from rabbits, rhesus monkeys, and humans. Specific activities were comparable to activities observed in several other extrahepatic tissues of rabbits and monkeys and in epidermal tissues from mice, but were one to two orders of magnitude lower than those observed in corresponding preparations of hepatic tissues. Cytochrome P-450 also could be detected in low concentrations in microsomal fractions of aortic wall homogenates. The monooxygenase activity found in the aorta could play a significant role in the etiology and pathogenesis of atherosclerosis in humans by catalyzing the conversion of environmental promutagens to mutagenic initiators and/or cytotoxic factors, thus leading to development of benign, smooth muscle tumors of the inner lining of artery walls.
A theorem on homogeneous functions and extended Cobb-Douglas forms
Authors: Charnes A. , Cooper W. W. , Schinnar A. P.
Published: May 2006

A form for homogeneous functions is presented which shows them to be a very simple extension of the wellknown Cobb-Douglas functions with similar properties in production (and distribution) economics. This form thus suggests new possibilities for interpreting a wide variety of empirical and theoretical results in economics; it also provides contact with developments in other fields, such as information theory and geometric programming.
Role of subunit interfaces in the allosteric mechanism of hemoglobin.
Authors: Chothia C , Wodak S , Janin J
Published: May 2006

We calculate the surface area buried in subunit interfaces of human deoxyhemoglobin and of horse methemoglobin. A larger surface area is buried in deoxy- than in methemoglobin as a result of tertiary and quaternary structure changes. In both molecules the dimer-dimer interface is closepacked. This implies that hydrophobicity stabilizes the deoxystructure, the free energy spent in keeping the subunits in a low-affinity conformation being compensated by hydrophobic free energy due to the smaller surface area accessible to solvent.
Synthesis and activities of neurotensin, and its acid and amide analogs: possible natural occurrence of [Gln4]-neurotensin.
Authors: Folkers K , Chang D , Humphries J , Carraway R , Leeman S E , Bowers C Y
Published: May 2006

It was considered, a priori, that the isolation of the tridecapeptide, neurotensin, might have inadvertently sllowed the hydrolysis of either the [Gln4]- or the [Leu13-NH2]-moieties. Neurotensin and its three acid and amide analogs, i.e., [Gln4]-neurotensin, neurotensin-NH2, and [Gln4]-neurotensin-NH2 were synthesized. Neurotensin and [Gln4]-neurotensin were indistinguishable by the hypotensive assay, hyperglycemic assay, contraction of the ileum, and radioimmunoassay. Neurotensin-NH2 and [Gln4]-neurotensin-NH2 showed less than 1% of these neurotensin activities. Present information does not elucidate whether the glutamic acid residue in position 4 of neurotensin in situ is present as Glu4 or as Gln4. At high levels, neurotensin released the luteinizing hormone, follicle stimulating hormone, and thyrotropin; [Gln4]-neurotensin-NH2 released thyrotropin, and [Gln4]-neurotensin released luteinizing hormone and follicle stimulating hormone, but these activities do not appear biologically significant.
Purification and characterization of 3':5'-cyclic GMP-dependent protein kinase.
Authors: Gill G N , Holdy K E , Walton G M , Kanstein C B
Published: May 2006

Guanosine 3':5'-cyclic monophosphate (cGMP)-dependent protein kinase has been purified to homogeneity from bovine lung by affinity chromatography and characterized. Partially purified protein kinase, specifically activated by low concentrations of cGMP (22 NM), was adsorbed onto 8-(2-aminoethyl)-amino-adenosine 3':5'-cyclic monophosphate-Sepharose. After washing to remove nonspecific proteins, cGMP-dependent protein kinase was specifically eluted by 0.1 mM cGMP. The purified protein contained cGMP-dependent protein kinase and specific cGMP binding activities. Purification of the holoenzyme was possible because subunit dissociation does not occur upon cyclic nucleotide binding. cGMP-dependent protein kinase holoenzyme has an apparent molecular weight of 150,000 as determined by glycerol density gradient sedimentation. On sodium dodecyl sulfate/polyacrylamide gel electrophoresis, a single protein band of 71,000 molecular weight was observed that suggested the holoenzyme is a dimer composed of subunits of identical molecular weight. cGMP-dependent protein kinase required high concentrations of Mg+2 for optimal activity; a heat-stable protein kinase modulator which inhibited adenosine 3':5'-cyclic monophosphate-dependent protein kinase activity had no effect on the activity of purified cGMP-dependent protein kinase.
Efficiency of energy transfer from photosystem II to photosystem I in
Porphyridium cruentum
Authors: Ley Arthur C. , Butler Warren L.
Published: May 2006

The yield of energy transfer from photosystem II to photosystem I in
Porphyridium cruentum
varies from a minimum value of about 0.50 when the photosystem II reaction centers are all open to a maximum value between 0.90 and 0.95 when the centers are all closed.
Nuclear magnetic resonance studies of the interaction of general anesthetics with 1,2-dihexadecyl-sn-glycero-3-phosphorylcholine bilayer.
Authors: Shieh D D , Ueda I , Lin H , Eyring H
Published: May 2006

Sonicated 1,2-dihexadecyl-sn-glycero-3-phosphorylcholine forms liposomes. Studies by Fourier transform proton magnetic resonance of the interaction of these bilayers with some general anesthetics, i.e., chloroform, halothane, methoxyflurane, and enflurane, show that the addition of a general anesthetic to the liposomes and raising the temperature have a similar effect in cuasing the fluidization of the bilayer. General anesthetics act on the hydrophilic site (choline group) in clinical concentrations and then diffuse into the hydrophobic region with the addition of larger amount of anesthetics. There is evidence that the lecithin choline groups are involved in the interaction with protein and that the general anesthetics change the conformation of some polypeptides and proteins. We conclude that the general anesthetics, by increasing the motion of positively charged choline groups and negatively charged groups in protein, weaken the Coulomb-type interaction and cause the liprotein conformational changes.
Relationship of gangliosides to the structure and function of thyrotropin receptors: their absence on plasma membranes of a thyroid tumor defective in thyrotropin receptor activity.
Authors: Fishman P H , Aloj S M , Kohn L D , Brady R O
Published: May 2006

Plasma membranes derived from rat thyroid tumor (1-8R) which is unresponsive to thyrotropin but is responsive to dibutyryl adenosine 3':5'-cyclic monophosphate bind less than 20% of the [125I] thyrotropin which can be bound to plasma membranes from normal rat thyroids under conditions which optimize tumor membrane binding relative to normal thyroid membranes. In addition, the binding is different from thyrotropin binding to normal thyroid membranes both in its altered sensitivity to changes in hydrogen ion concentration and in a decreased sensitivity to competition by unlabeled thyrotropin. This reduced capacity to bind [125I] thyrotropin cannot be attributed to degradation of the hormone by membrane-associated proteases. Although the supernatant phase of the thyroid tumor homogenates contains a soluble component which inhibits [125I] thyrotropin binding to thyrotropin receptors on plasma membranes, its level is the same as in homogenates of normal thyroid tissue. Trypsin digestion does not expose thyrotropin receptors in a manner analogous to that seen in normal thyroid tissue. The major ganglioside in the tumor membranes is N-acetylneuraminylgalactosylglucosylceramide and the membranes lack the N-acetylgalactosaminyltransferase required for the synthesis of more complex gangliosides. In contrast, the normal rat thyroid membranes contain more complex gangliosides such as galactosyl-N-acetylgalactosaminyl-[N-acetylneuraminyl]-galactosylglucosylceramide and N-acetylneuraminylgalactosyl-N-acetylgalactosaminyl-[N-acetylneuraminyl]-galactosylglucosyl ceramide as well as the glycosyltransferase activities required for their syntheses. Galactosyl-N-acetylgalactosaminyl-[N-acetylneuraminyl]-galactosylglucosylceramide can also be detected in normal membranes, but not in tumor membranes, by selective labeling with galactose oxidase (D-galactose: oxygen 6-oxidoreductase, EC 1.1.3.9) and [3H] sodium borohydride. These results support the hypothesis that gangliosides are important structural or functional components of thyrotropin receptors on thyroid plasma membranes.
Calculation of immigration and extinction curves from the species-area-distance relation
Authors: Gilpin Michael E. , Diamond Jared M.
Published: May 2006

Quantitative models of the species-area-distance relation, based on equilibria between immigration and extinction rates, have been tested against data for birds on 52 Solomon islands. Biologically reasonable models account for 98% of the variance in species number. The data are adequate to permit determination of immigration and extinction curves and the values of seven associated parameters. The resulting curves are very concave. Extinction rates vary almost exactly as the reciprocal of area, but the effect of area on immigration rates is slight. Recognition of major differences among species in immigration and extinction rates and in dispersal distances proves essential to a successful model.
Oligomeric intermediate in peptidoglycan biosynthesis in Bacillus megaterium.
Authors: Fuchs-Cleveland E , Gilvarg C
Published: May 2006

An oligomeric intermediate in the biosynthetic pathway of peptidoglycan was isolated from B. megaterium. The oligomer has been identified as [disaccharide(pentapeptide)]12 pyrophosphoryl undecaprenol.
Free acid, anion, alkali, and alkaline earth complexes of lasalocid a (X537A) in methanol: structural and kinetic studies at the monomer level.
Authors: Shen C , Patel D J
Published: May 2006

We report below on nuclear magnetic resonance investigations of the structure and exchange kinetics for the free acid, anion, sodium complex, and barium complex of the ionophore lasalocid A (X537A) in methanol solution. A comparison between the proton and carbon longitudinal relaxation times of lasalocid in nonpolar and polar solvents demonstrates that the free acid (HX) is a monomer in methanol solution. Parallel proton and carbon relaxation measurements demonstrate that the anion (X-), sodium complex (NaX), and barium complex (BaX+) are also monomeric in methanol solution. These results are in contrast to the Na2X2 dimer and the BaX2-H20 dimer observed in crystals and in nonpolar (cyclohexane and methylene chloride) solutions. Large downfield shifts on complex formation (X- to NaX and BaX+) are detected for protons located on the polar face of the ionophore with their C-H bonds directed towards and proximal to the metal ion. The exchange of lasalocid anion between free (X-) and complexed (BaX+) states in methanol can be monitored from the temperature-dependent line shapes of the proton resonances at superconducting fields. The exchange rates are independent of the reactant concentrations and are characteristic of a rate-determining dissociation of BaX+ in methanol solution with activation parameters delta H++ = 6.5 kcal mol-1 (25 degrees) and delta S++ = -20.0 cal mol-1 degree -1 (1 cal = 4.184 J). The rate constants for dissociation and formation of BaX+ complex in methanol, 25 degrees, are 5.2 X 10(3) sec-1 and 1.5 X 10(10) M-1 sec-1, respectively. These studies were extended to derive the activation parameters for the exchange of lasalocid anion between BaX+ and NaX and between BaX+ and HX in methanol, while the exchange among HX, X-, and NaX is too rapid to be monitored on the time scale of nuclear magnetic resonance.
Binding of triton X-100 to diphtheria toxin, crossreacting material 45, and their fragments.
Authors: Boquet P , Silverman M S , Pappenheimer A M , Vernon W B
Published: May 2006

Binding of the nonionic detergent [3H]Triton X-100 by diphtheria toxin, by the nontoxic serologically related protein crossreacting material (CRM) 45, and by their respective A and B fragments has been studied. If first denatured in 0.1% sodium dodecyl sulfate, all of the proteins with the exception of fragment A bind increasing amounts of Triton X-100, reaching a maximum of more than 40 mol bound per mol of protein when the detergent concentration exceeds its critical micelle concentration. No measurable amount of Triton X-100 is bound by native toxin or its A fragment of any concentration of the detergent. Undenatured CRM45 or its B45 fragment, on the other hand, readily became inserted into Triton X-100 micelles when the detergent reaches its critical micelle concentration. The results show that the toxin molecule contains a hydrophobic domain located on the portion of the B fragment that is linked to A. This region is masked in native toxin. Based on these findings, a model is proposed to describe how fragment B facilitates the transport of the enzymically active hydrophilic fragment A across the plasma membrane to reach the cytoplasm.
Inhibition and stimulation of the development of the bioluminescent system in Beneckea harveyi by cyclic GMP.
Authors: Ulitzur S , Yashphe J , Hastings J W
Published: May 2006

The development of the luminescence system in Beneckea harveyi is controlled by cyclic nucleotides at the level of transcription. In the wild type, it is repressed by exogenously added guanosine 3':5'-cyclic monophosphate and this repression is overcome by the addition of adenosine 3':5'-cyclic monophosphate. These observations alone support a model in which these nucleotides act antagonistically. On the other hand, in a mutant requiring adenosine 3':5'-cyclic monophosphate for maximum luminescence, guanosine 3':5'-cyclic monophosphate stimulates the synthesis of the luminescence system at low concentrations and inhibits it at higher concentrations. These results are apparently not consistent with a model involving a simple antagonistic effect of guanosine 3':5'-cyclic monophosphate on the action of adenosine 3':5'-cyclic monophosphate.
Assignment of a locus required for flavoprotein-linked monooxygenase expression to human chromosome 2.
Authors: Brown S , Wiebel F J , Gelboin H V , Minna J D
Published: May 2006

Hybrid clones segregating human chromosomes were prepared by fusing mouse RAG cells to fresh human bone marrow cells and tested for the mixed-function oxygenase [flavoprotein-linked monooxygenase; RH, reduced-flavoprotein:oxygen oxidoreductase (RH-hydroxylating); EC 1.14.14.1] arylhydrocarbon hydrocarbon hydroxylase. Neither constitutive nor induced aryl hydrocarbon hydroxylase activity was detected in parental RAG cells. Induced aryl hydrocarbon hydroxylase was expressed in 4 out of 12 primary and 12 out of 19 secondary hybrid clones examined. Constitutive hydroxylase activity was detectable in 9 of the 15 inducible clones. All of the hybrid clones that exhibited constitutive hydroxylase activity were also inducible. There was a positive correlation between constitutive and induced hydroxylase activities although the absolute levels of the enzyme showed a wide range between different clones. Isozyme analysis performed on 12 primary and 19 secondary hybrid clones showed that aryl hydrocarbon hydroxylase activity was concordant with the expression of the human isozymes malate dehydrogenase (EC 1.1.1.37) and isocitrate dehydrogenase (EC 1.1.1.42), previously assigned to human chromosome 2. Isozyme markers for 19 other human chromosomes segregated independently from aryl hydrocarbon hydroxylase activity. The results suggest that the gene(s) required for aryl hydrocarbon hydroxylase activity are located on human chromosome 2.
Opiate and stimulus-produced analgesia: functional anatomy of a medullospinal pathway.
Authors: Basbaum A I , Clanton C H , Fields H L
Published: May 2006

Neurons in ventromedial medulla, including the nucleus raphe magnus, project to trigeminal nucleus caudalis and, via the dorsolateral funiculus, to spinal dorsal horn. The terminals of this descending system are in loci containing cells responsive to noxious stimuli. Electrical stimulation of nucleus raphe magnus selectively inhibits spinal dorsal horn neurons that respond to noxious stimuli. These neurons are located near the anatomically demonstrated terminals of this descending system. Dorsolateral funiculus lesions block this descending inhibition of spinal neurons as well as the analgesic action of morphine. This evidence supports the hypothesis that this neuron population mediates the analgesia produced by opiates and electrical stimulation of certain diencephalic and brainstem sites.
Solar abundance of iridium
Authors: Drake Stephen , Aller Lawrence H.
Published: May 2006

By a method of spectrum synthesis, which yields log
gfA
, where
g
is the statistical weight of the lower level,
f
is the oscillator strength, and
A
is the abundance, an attempt is made to deduce the solar iridium abundance from one relatively unblended, but fairly weak IrI line, λ 3220.78 Å. If the Corliss-Bozman
f
-value for this line is adopted, we find log
A
(Ir) = 0.82 on the scale log
A
(H) = 12.00. The discordance with the value found from carbonaceous chondrites may arise from faulty
f
-values or from difficulties arising from line blending in this far ultraviolet domain of the solar spectrum.
Detection of polycistronic and overlapping bacteriophage T7 late transcripts by in vitro translation.
Authors: Pachl C A , Young E T
Published: May 2006

Bacteriphage T7 RNAs have been fractionated on preparative polyacrylamide gels. The in vitro coding capacities of the RNAs have been determined by translation of the RNAs in a cell-free system and analysis of the polypeptide products on sodium dodecyl sulfate polyacrylamide slab gels. The T7 early RNAs are fractionated according to their molecular weight and without intermolecular aggregation. Fractionation of the late T7 RNAs gives rise to 10 major RNAs, ranging in size from 0.29 X 10(6) daltons to 2.05 X 10(6) daltons. Five of these RNAs are polycistronic and overlapping species are present for some T7 proteins. In particular, the gene 10 protein, the major capsid protein, is translated from at least three mRNAs. The smallest of these gene 10 mRNAs is monocistronic. A second gene 10 mRNA also codes for the gene 9 protein, and a third gene 10 mRNA codes for both gene 8 and gene 9 proteins. The T7 gene 3.5 protein, a T7 lytic enzyme, is also translated from several differently sized mRNAs. Comparison with published data on in vitro transcription by T7 RNA polymerase suggestes that transcription from multiple initiation sites and cleavage of larger precursors are both involved in generating the late T7 transcripts we observe. The overlapping mode of transcription could serve to amplify certain gene products.
Partial purification of a serum factor that causes necrosis of tumors.
Authors: Green S , Dobrjansky A , Carswell E A , Kassel R L , Old L J , Fiore N , Schwartz M K
Published: May 2006

Tumor necrosis can be induced in transplanted mouse methylcholanthrene-induced sarcoma by a tumor necrosis factor in the serum of mice infected with bacillus Calmette-Guérin and given bacterial endotoxin. Sera from normal mice, endotoxin-treated mice, and mice infected with bacillus Calmette-Guérin do not contain this factor. A 20- to 30-fold purification of the serum factor has been achieved by (NH4)2SO4 fractionation, Sephadex G-100 and G-200 gel filtration, and preparative polyacrylamide electrophoresis. Tumor necrosis factor is not bacterial endotoxin. It migrates with alpha-globulins, is made up of at least four subunits, and has a molecular weight of about 150,000. The active factor is a glycoprotein that contains sialic acid and galactosamine.
Glutathione and gamma-glutamyl cycle enzymes in crypt and villus tip cells of rat jejunal mucosa.
Authors: Cornell J S , Meister A
Published: May 2006

Villus tip cells and crypt cells of rat jejunal mucosa were separated by the planning procedure of Imondi et al. and were studied with respect to their activities of the enzymes of the gamma-glutamyl cycle and glutathione content. The villus tip cells exhibit much higher gamma-glutamyl transpeptidase activities than do the crypt cells: thus, gamma-glutamyl trnaspeptidase appears to be a villus-specific enzyme. gamma-Glutamyl cyclotransferase and the enzymes required for glutathione synthesis are not specifically localized to either the crypt or villus tip cells but are present in both. The crypt cells have a high concentration of glutathione (4-5 mM) comparable to the levels found in liver and kidney; in contrast, the villus tip cells have much lower concentrations. On fasting, the glutathione concentration decreased markedly in both villus tip and crypt cells; feeding of protein, but not of sucrose, led to increased glutathione concentrations. The migration of cells from the undifferentiated crypt cell region to the villus tip is associated with structural and biochemical changes that equip the cell for its mature functional activities, which include transport. The present findings indicate that such cellular differentiation and migration is associated with a marked increase in gamma-glutamyl transpeptidase activity and in the utilization of glutathione.
Primary structure determination of two cytochromes c2: close similarity to functionally unrelated mitochondrial cytochrome C.
Authors: Ambler R P , Meyer T E , Kamen M D
Published: May 2006

The amino-acid sequences of the cytochromes c2 from the photosynthetic non-sulfur purple bacteria Rhodomicrobium vannielii and Rhodopseudomonas viridis have been determined. Only a single residue deletion (at position 11 in horse cytochrome c) is necessary to align the sequences with those of mitochondrial cytochromes c. The overall sequence similarity between these cytochromes c2 and mitochondrial cytochromes c is closer than that between mitochondrial cytochromes c and the other cytochromes c2 of known sequence, and in the latter multiple insertions and deletions must be postulated before a match can be obtained. Nevertheless, these two cytochromes c2 show no better reactivity with the mitochondrial cytochrome c oxidase than do the less well-matched cytochromes c2. The bearing of these findings on possible evolutionary relationship between mitochondria and prokaryotes is discussed.
Structure-function relations in hemoglobin as determined by x-ray absorption spectroscopy.
Authors: Eisenberger P , Shulman R G , Brown G S , Ogawa S
Published: May 2006

Conclusions concerning the structure around the iron atom in oxy- and carbonmonoxyhemoglobin have been obtained by fluorescent x-ray absorption studies. The bis-imidazole heme complex was used as a model system of known structure. The ligated forms of hemoglobin, and cytochrome c at high pH, gave spectra which were very similar to the bis-imidazole complex, where the average Fe-N bond distance is known to be 1.98 A. By comparison it was possible to determine that the average Fe-N bond distances were 1.99 A in oxyhemoglobin, 1.98 A in carbonmonoxyhemoglobin, and 1.98 A in cytochrome c at pH less than 10.5, with an experimental accuracy of +/-0.02 A. An experimental comparison between oxy- and deoxyhemoglobin A showed much larger spectral changes than amongst the ligated forms. A comparison was made between the low oxygen affinity form of deoxy HbA and the high affinity form of doexy Hb Kempsey (alpha2beta992 Asp leads to Asn). All the spectral features coincided, allowing us to conclude that the average iron-ligand bond differences must be less than or equal to 0.02 A. Since the strain energy is proportional to the square of this displacement, we show that the strain energy at the iron is less than or equal to 4 X 10(-3) eV. This is negligible compared to the difference of binding energy of the high and low affinity forms, which is 0.15 eV, showing that the energies responsible for the increase of oxygen affinity are not localized at the heme.
Chitin biosynthesis during Blastocladiella zoospore germination: evidence that the hexosamine biosynthetic pathway is post-translationally activated during cell differentiation.
Authors: Selitrennikoff C P , Allin D , Sonneborn D R
Published: May 2006

De novo construction of a chitinous cell wall accompanies Blastocladiella emersonii zoospore germination. At least an order of magnitude increase in total hexosamine occurs during germination. This increase is into polymer (chitin) and occurs on schedule in the presence of cycloheximide. Uridine-5'-diphospho-N-acetylglucosamine (UDPGlcNAc), both the end product of hexosamine biosynthesis and a substrate for chitin biosynthesis, is a potent inhibitor of the activity of the first pathway-specific enzyme of hexosamine biosynthesis in zoospore extracts. Certain uridine nucleotides, not perceptibly influencing the activity of the first enzyme per se, counteract the inhibitory effects of UDPGlcNAc. The concentration of UDPGlcNAc in the zoospore is sufficient to act as an inhibitor of the enzyme, but the amount of UDPGlcNAc is sufficient, by over an order of magnitude, to account for the chitin synthesized during germination. Both the production of UDPGlcNAc and its utilization for chitin synthesis appear to be post-translationally regulated in zoospores and during zoospore germination.
Mechanisms of adhesion among cells from neural tissues of the chick embryo.
Authors: Rutishauser U , Thiery J P , Brackenbury R , Sela B A , Edelman G M
Published: May 2006

In order to analyze the molecular mechanisms of cell adhesion during development, proteins on the surface of chick embryonic neural cells were compared with proteins released after placing these cells in culture. One of the components released into culture, F1 (molecular weight, Mr 140,000), was derived by proteolytic cleavage of a cell surface precursor with a molecular weight of at least 240,000. Another protein, F2, recovered from culture as a dimer (Mr 1110,000), appeared to be a product of limited proteolytic cleavage of F1. Cells in retinal tissue possessed a surface protein of Mr 150,000 that also appeared to be derived by limited proteolytic cleavage of the cell surface precursor. Antibodies to F2 interacted with determinants on the cell surface protein of Mr 150,000, and specifically prevented homologous and heterologous binding among dissociated retinal and brain cells. In contrast, antibodies to F1 failed to prevent cell-cell adhesion and did not crossreact with F2. These data suggest that the cell surface protein of Mr 150,000 generated by limited proteolysis is involved in adhesion of both retinal and brain cells. Cell-cell binding of both retinal and brain cells varied as a function of developmental age and brain cells acquired their binding properties at an earlier time than retinal cells. Similar results were obtained in experiments on the binding of retinal and brain cells of different ages to nylon fibres coated with antibodies to F2. The results of the molecular and cellular experiments are incorporated in a model for cell adhesion invoking both proteolytic activation and modulation of cell surface ligands.
Menkes disease: a biochemical abnormality in cultured human fibroblasts.
Authors: Goka T J , Stevenson R E , Hefferan P M , Howell R R
Published: May 2006

Cultured skin fibroblasts from patients with Menkes disease, an X-linked disorder involving a defect in copper metabolism, were analyzed for copper concentration by means of atomic absorption spectrophotometry. These cultures consistently exhibited elevated copper concentrations (mean = 335.5 ng of copper per mg of protein) when compared to control fibroblast cultures (mean = 59.2 ng of copper per mg of protein). External factors that could influence the copper content of cultures were found not to affect the differences in copper concentration between control and Menkes cells. Furthermore, Menkes cells could be differentiated from cultured fibroblasts of controls, of presumed heterozygotes, and of Wilson's disease patients by copper concentration. These observations led to the conclusion that the increased copper content of cultured Menkes cells was characteristic of Menkes disease, resulting from the expression of the genetic abnormality. This provides a genetic marker, a defect in metal metabolism demonstrated in human fibroblasts, that should prove valuable in both the diagnosis of Menkes disease and in the study of the fundamental defect of this genetic disorder.
Inhibition of cell-mediated cytolysis of trinitrophenyl-derivatized target cells by alloantisera directed to the products of the K and D loci of the H-2 complex.
Authors: Burakoff S J , Germain R N , Dorf M E , Benacerrah B
Published: May 2006

The role of the products of the K and D loci of the H-2 complex as target antigens for cytotoxic T cells generated to modified syngeneic cells has been investigated. Spleen cells, when cocultured with trinitrophenyl-derivatized syngeneic cells, generate cytolytic T cells that lyse most effectively tumor or spleen targets that are trinitrophenyl-derivatized and H-2 identical to the sensitizing cell. Cytolysis is inhibited by alloantisera to the K and/or D specificities of the target cells and by anti-dinitrophenyl antisera. Cytolic cells generated in this manner are also able to lyse, though less efficiently, trinitrophenyl-derivatized tumor and spleen targets that do not share products of the K and D loci with the sensitizing cell, and this cytolysis is also blocked by alloantisera directed to the H-2 serological specificities of such targets.
Stucture of the amino-acid accepting 3'-end of high-molecular-weight eggplant mosaic virus RNA.
Authors: Briand J P , Richards K E , Bouley J P , Witz J , Hirth L
Published: May 2006

The sequence of the first 59 nucleotides from the 3'-OH terminus of high-molecular-weight eggplant mosaic virus RNA has been determined by standard radio-chemical techniques. The fragment was identified among the products of partial T1 RNase digestion by making use of the reverse migration, at pH 2.5, of the 3'-OH terminal oligonucleotide. No abnormal bases were found. A model of secondary structure may be constructed for this fragment, which is known to fix valine in the presence of valyl-tRNA synthetase. Its relation to the structures of genuine tRNAs and to the 3'-OH termini of other viral RNAs that also accept amino acids is discussed.