bluuebunny/crossref_metadata_2025_split huggingface dataset:
Properties of the Interaction of the Sodium Channel with Permeant Monovalent Cations
Authors: JACQUES Yannick , ROMEY Georges , FOSSET Michel , LAZDUNSKI Michel 
Published: July 2010

The use of sea anemone toxin, veratridine and scorpion toxin which specifically interact with the gating system of the sodium channel and maintain the channel in an open conformation has permitted a study of the mechanism of transport of monovalent cations through the selectivity filter of this channel. The initial rate of 22Na+ influx through the tetrodotoxin‐sensitive Na+ channels of excitable cells is dependent upon the external concentrations of Na+ and Na+‐substitutes with the following properties. (a) It is saturable at high Na+ concentrations and increases with the external Na+ concentration in a cooperative manner (nH= 1.6). (b) At low external Na+ concentrations (1 mM), it is activated and then inhibited by increasing external concentrations of monovalent cations such as Li+, guanidinium, hydrazinium, hydroxylamine and K+. The activating effect of these cations disappears at higher external Na+ concentrations (10 mM).The experimental data are consistent with a model involving at least two allosteric cation‐binding sites per Na+ channel. The binding of monovalent cations to Na+ sites is characterized by a high positive homotropic cooperativity.Most of the work describes the properties of the Na+ channel in neuroblastoma cells. The mechanism has also been shown to be valid for excitable cells of other types and origins.
Stereochemistry of the Conversions of l‐Threonine and d‐Threonine into 2‐Oxobutanoate by the l‐Threonine and d‐Threonine Dehydratases of Serratia marcescens
Authors: CROUT David H. G. , GREGORIO Maria V. M. , MÜLLER Urs S. , KOMATSUBARA Saburo , KISUMI Masahiko , CHIBATA Ichiro 
Published: July 2010

dl[3‐2H]Threonine, l‐[3‐2H]threonine, (2RS,3S)‐2‐amino[3‐2H1] butanoic acid, (2RS,3S) 2‐amino[3‐3H1]butanoic acid and dl‐2‐amino[3‐14C]butanoic acid were synthesised.
l‐[3‐2‐H]Threonine was converted into l‐[4‐2H1]isoleucine by Serratia marcescens strain IHr313.
(2RS,3S)‐2‐Amino[3‐2‐H1]butanoic acid was converted into l‐[4‐4‐H1]isoleucine by S. marcescens strain 149.
Analysis by 220‐MHz NMR spectroscopy of the labelled l‐isoleucine produced showed that the same diastereotopic hydrogen at C‐4 was labelled in each experiment, proving that, during the conversion of l‐threonine into 2‐oxobutanoate mediated by biosynthetic l‐threonine dehydratase, the hydroxyl group at C‐3 was replaced by hydrogen with retention of configuration.
S. marcescens strain 149 lacks l‐threonine dehydratase but possesses an inducible d‐threonine dehydratase. This strain converted dl‐[3‐2H]threonine into dl‐[4‐2H1]isoleucine with the deuterium located in the diastereotopic C‐4 hydrogen derived from the 3 pro‐R hydrogen of 2‐aminobutanoic acid.
This result proved that during the conversion of d‐threonine into 2‐oxobutanoate mediated by d‐threonine dehydratase, the hydroxyl group at C‐3 is replaced by hydrogen with retention of configuration.
These results also prove that the protonation at C‐3 of the proposed enamine intermediate in the transformations catalysed by threonine dehydratase is under enzymatic control.
The present results, taken in conjunction with the independent assignment of the signals in the 220‐MHz NMR spectrum of l‐isoleucine due to the diastereotopic protons at C‐4, prove that during the ethyl migration step in l‐isoleucine biosynthesis, the configuration at the migrating centre is retained.
Dark Isomerization of Retinals in the Presence of Phosphatidylethanolamine
Authors: GROENENDIJK Gerard W. T. , JACOBS Cor W. M. , BONTING Sjoerd L. , DAEMEN Frans J. M. 
Published: July 2010

Dark incubation of retinoids (retinyl ester, retinol, retinal, retinaloxime) in suspensions of rod outer segment membranes leads to substantial isomerization (and partial degradation) in the case of retinals only.
All‐trans, 13‐cis and 9‐cis‐retinal all isomerize at the Δ13 double bond leading to an equilibrium with approximately 75%trans and 25%cis isomer at this bond (all‐trans⇔ 13‐cis and 9‐cis⇔ 9,13‐dicis).11‐cis‐Retinal isomerizes irreversibly to a mixture of all‐trans and 13‐cis‐retinal.
The active compound appears to be phosphatidylethanolamine present in the membrane. The amino group and the phosphate, as well as the hydrophobic part of the phospholipid are essential.
At least three factors are important for the phosphatidylethanolamine‐catalyzed isomerization as studied with the 13‐cis isomer: the concentration of phosphatidylethanolamine, the concentration of Schiff base between retinal and phosphatidylethanolamine and the presence of lipid aggregates.
Based on these observations a mechanism is proposed, which satisfactorily explains the specificity of the isomerization pattern.
It is suggested that reisomerization of all‐trans to 11‐cis retinal in vivo takes place by fixation of all‐trans retinal on an adequate surface (e.g. opsin) and a localized nucleophilic attack on the C‐11 atom, followed by trapping of the isomerized chromophore by opsin.
It is further concluded that retinal does not occur in vivo as a free intermediate. Direct transfer from one protein to another (opsin, retinol dehydrogenase, retinal binding proteins) seems to take place.
Nucleotide Sequence of the Simian Virus 40 HindII + III Restriction Fragment A (Second Part of the T Antigen Gene)
Authors: VOLCKAERT Guido , VAN DE VOORDE André , FIERS Walter 
Published: July 2010

The nucleotide sequence of the second part of the simian virus 40 DNA HindII + III restriction fragment A is presented. The sequence extends from map position 0.533 to 0.424 and together with the first part of Hind‐A [Volckaert et al. Proc. Natl Acad. Sci. U.S.A. 75, 2160–2164 (1978)] completes the total Hind‐A sequence, comprising 1169 base pairs. The second half of Hind‐A includes the region corresponding to the second splicing boundary common to small tumor antigen (small‐t) and large tumor antigen (large‐T) mRNA and it contains coding information for an internal portion of large‐T antigen. Two similar secondary structures of reasonable thermodynamic stability can be proposed for the nucleotide sequence of the pre‐mRNA corresponding to the region reported here. Their possible relevance to the splicing of the SV40 early mRNAs is discussed.The deduced amino acid sequence is 188 residues long and contains a Lys‐Lys‐Lys‐Arg‐Lys stretch which may be involved in the DNA binding capacity of large‐T. A presumptive phosphorylation site is also present.
Nucleotide Sequence of the Simian Virus 40 HindII + III Restriction Fragment I (Fourth Part of the T Antigen Gene)
Authors: VAN HERREWEGHE Jacqueline , VAN DE VOORDE André , FIERS Walter 
Published: July 2010

The HindII + III restriction fragment I (Hind‐I) from simian virus 40 DNA represents 4.96% of the genome and maps in the early transcription region. Hind‐I is an internal segment of the A gene and its information is expressed as part of the early 19‐S mRNA, which codes for T antigen. We report here the nucleotide sequence of the 259‐base‐pair Hind‐I fragment. The sequence was determined and confirmed by RNA and DNA sequencing methods: by analysis of oligonucleotides resulting from T1 and pancreatic RNase digestion of labeled RNA transcribed from SV40 DNA with Escherichia coli DNA‐dependent RNA polymerase, by partial degradation of RNA transcripts with snake venom phosphodiesterase, and by base‐specific chemical degradation of 5′‐end‐labeled subfragments of Hind‐I according to the procedure of Maxam and Gilbert.Multiple triplets corresponding to termination codons occur in two of the three reading frames of the DNA strand that has the same polarity as early mRNA. The open reading frame connects in phase with the one of the Hind fragments flanking Hind‐I, and the amino acid sequence specified by Hind‐I lies in the middle part of the large‐T antigen. Some features of the primary nucleotide sequence and of early transcription are discussed.
Nucleotide Sequence of the Hind‐I‐proximal Part of Simian Virus 40 HindII + III Restriction Fragment B. Fifth Part of the T Antigen Gene
Authors: VAN HERREWEGHE Jacqueline , VAN DE VOORDE André , FIERS Walter 
Published: July 2010

The nucleotide sequence of the simian virus 40 DNA segment that lies between the HindIII restriction endonuclease cleavage site at map position 0.324 and the AtuI cleavage site at 0.261 has been determined by the base‐specific partial chemical degradation procedure of Maxam and Gilbert. This region comprises 335 base pairs and represents 6.4% of the total SV40 genome and 41% of the restriction fragment Hind‐B. It connects in the clockwise direction to the restriction fragment Hind‐I (described in the preceding paper). Hind‐B is situated in the second half of the early transcription region of the SV40 genome and encodes information (including the termination signal) for the early protein large‐T antigen. In the part of Hind‐B described here, the DNA strand that has the same polarity as early 19‐S mRNA defines only one open reading frame for translation; the other two are blocked by multiple triplets corresponding to termination codons. The open reading frame is part of one that runs throughout much of the early region: from the second splicing boundary of the large‐T gene (position 0.534) to the information for the large‐T stop signal (position 0.174) near the Hind‐B/Hind‐G junction, and which together with the non‐contiguous DNA segment from position 0.65 (site of the information for the large‐T start signal) to 0.60 (the first splicing boundary) codes for the entire large‐T antigen.
Nucleotide Sequence of Simian Virus 40 DNA: Structure of the Middle Segment of the HindII + III Restriction Fragment B (Sixth Part of the T Antigen Gene and Codon Usage)
Authors: VAN HEUVERSWYN Hugo , VAN DE VOORDE André , VAN HERREWEGHE Jacqueline , VOLCKAERT Guido , DE WINNE Paul , FIERS Walter 
Published: July 2010

We report here the nucleotide sequence of the simian virus 40 DNA region that lies between the EcoRII restriction endonuclease cleavage sites at map positions 0.214 and 0.281. The sequence was determined by partial chemical degradation of terminally labeled DNA fragments according to the procedure of Maxam and Gilbert. This region represents 6.7% of the SV40 genome and is located in the middle of HindII + III restriction fragment B. It is expressed as part of the early 19‐S messenger RNA, which codes for the large‐T antigen protein. Only one open reading frame for translation can be deduced from the message strand of the DNA and this reading frame connects in phase with the one of both neighboring fragments.This publication is the last in a series of papers about the T‐antigen gene, and several properties of this gene and its product are discussed. The non‐randomness of codon usage is similar to that previously discussed for the late part of the genome. Moreover, it appears that the choice of a third letter can be determined by the nature of the following codon; some codons which start with a pyrimidine are almost never preceded by an adenosine and some ANN‐type codons are almost never preceded by a guanosine.
Variable Rate of Polypeptide Chain Elongation in vitro
Authors: ABRAHAM Abraham K. , PIHL Alexander 
Published: July 2010

Translation of rabbit globin mRNA and tobacco mosaic virus mRNA was studied in a wheat germ system. After a short pulse with labeled methionine, the reaction products were separated by polyacrylamide gel electrophoresis in sodium dodecyl sulfate and visualized by fluorography. Discrete bands corresponding to incomplete products were detected both with globin and tobacco mosaic virus RNA as messenger at a time when no release of peptides from tRNA could be detected.In the absence of spermidine certain intermediate products accumulated during the chase period.With increasing incubation time, the radioactivity of most bands was chased into higher‐molecular‐weight products. This change in size distribution was more pronounced when magnesium was partially replaced by spermidine.Evidence is presented that some of the incomplete products had in part been released from tRNA. No such release of polypeptides could be detected in experiments using the artificial messenger poly(U), indicating that non‐specific peptidyl‐tRNA hydrolases were not present in the system.The transient accumulation of discrete bands during the chase period indicates that in the wheat germ system polypeptide chain elongation occurs at discontinuous rates. The fact that spermidine increases the rate of elongation and the yield of full‐length translation products may be due to its ability to facilitate the movement of the ribosomes beyond regions where the elongation is retarded.
The Primary Structure of the Phosphatidylcholine‐Exchange Protein from Bovine Liver
Authors: MOONEN Peter , AKEROYD Robert , WESTERMAN Jan , PUIJK Wouter C. , SMITS Petrus , WIRTZ Karel W. A. 
Published: July 2010

The phosphatidylcholine exchange protein from bovine liver consists of a single polypeptide chain and has a blocked N terminus. The protein contains an estimated 244 amino acid residues in accordance with a determined molecular weight of 28000. The protease from mouse submaxillaris gland cleaved the citraconylated and S‐carboxymethylated derivative of the exchange protein at one specific site (Arg14‐Glu15) close to the N terminus. Analysis of the two resulting peptides showed that N‐acetyl‐methionine was the N‐terminal residue and gave the sequence of the first 41 residues.The modified protein was also fragmented with the protease from Staphylococcus aureus. The peptides isolated represented 88% of the protein; their sequences were determined by manual and automated Edman degradation. Alignment of a number of these peptides gave the complete sequence of the N‐terminal half up to position 122.
Reactivity of the Thiol Group in Human and Bovine Albumin at pH 3–9, as Measured by Exchange with 2,2′‐Dithiodipyridine
Authors: PEDERSEN Anders Overgaard , JACOBSEN Jørgen 
Published: July 2010

The kinetics for exchange between an aromatic disulphide and the thiol group in human and bovine albumin as well as in glutathione were investigated in the pH range 2.5–9.8.For both albumins the rate constants exhibit a maximum near pH 3, confirming the results of Svenson and Carlsson's investigation of bovine albumin [A. Svenson and J. Carlsson (1975) Biochim. Biophys Acta, 400, 433–438]. This was related to the well known N–F conformational change of the protein.At pH 5–8 the reactivity of the thiol group in both albumins and glutathione changes sharply, probably due to ionization of the thiol group. At pH above 8, however, the reactivity of the thiol group in albumins, but not in glutathione, becomes nearly independent of pH.In addition, a conformational change at pH 6.5–8.5 was studied by means of differential spectroscopy of bilirubin, liganded to human albumin. This neutral transition appeared to proceed identically in mercaptalbumin and nonmercaptalbumin.It is concluded that (a) the pK of the thiol group in albumin is significantly below that of SH in glutathione, and (b) ionization of this thiol group, Cys‐34, is independent of the neutral transition.
Regulatory Effects of Iodide and Thiocyanate on Tyrosine Oxidation Catalyzed by Thyroid Peroxidase
Authors: MICHOT Jean‐Luc , OSTY Jeannine , NUNEZ Jacques 
Published: July 2010

The effects of iodide, thiocyanate and perchlorate, three anions with the same molecular size, on the oxidation of tyrosine to 3,3′‐bityrosine by several peroxidases were evaluated at pH 8.8, i.e. in conditions in which iodide is not oxidized. The following results were obtained:

Iodide greatly stimulates the rate of bityrosine formation in the presence of thyroid peroxidase. No effect was seen with horseradish peroxidase or lactoperoxidase. Maximal iodide effects were obtained with about 0.5 mM iodide and Km for iodide was equal to about 0.028 mM. These results suggest that thyroid peroxidase contains a simple class of regulatory binding sites for iodide.
SCN− mimics iodide effects; maximal stimulatory effects were seen with about 0.5 mM thiocyanate and Km for SCN− was equal to 0.1 mM. The effects of SCN− and those of iodide were not additive. These results suggest that SCN− binds to the same regulatory site as iodide but with a slightly lower affinity. No effect of SCN− was seen with horseradish peroxidase or lactoperoxidase.
ClO−4, another anion with the same molecular size as iodide and SCN−, had neither an effect on the oxidation of tyrosine to bityrosine nor did it prevent the stimulatory effect of iodide on this reaction. Bromide was without effect on the same reaction.
Pyridine Nucleotide Transhydrogenase from Azotobacter vinelandii
Authors: VOORDOUW Gerrit , VAN DER VIES Saskia , SCHOLTEN Jan Willem , VEEGER Cees 
Published: July 2010

Purified transhydrogenase from Azotobacter vinelandii forms very stable polymers at neutral pH. These show little tendency to dissociate upon dilution but can be disoociated by raising the pH.
The stability of transhydrogenase polymers towards dilution can be demonstrated with enzyme that is in part covalently bound to Sepharose. Non‐covalently bound subunits are kept bound upon elution at pH 7.5 and can only be released by raising the pH of the eluting buffer (pH 9.0). The remaining dissociated immobilized polymers can be reconstituted by adding free transhydrogenase at a lower pH (7.5–8.5). Reconstitution of dissociated immobilized A. vinelandii polymers can also be achieved with enzyme from Pseudomonas aeruginosa, which demonstrates the close structural relationship between these two enzymes.
Differential centrifugation of cell suspensions lysed with the osmotic shock method in the presence of EDTA shows transhydrogenase to be present largely as the non‐polymerized octamer (S20,w= 15 S). However, the distribution of the enzyme activity changes markedly when divalent cations (MgCl2, CaCl2) are included in the lysis buffer: up to 65% of the transhydrogenase activity then co‐sediments with membranes and nucleic acids (30 min, 20000 × g). Nuclease treatment leads to disappearance of the rapidly sedimenting transhydrogenase fraction. These results are incompatible with a reversible divalent‐cation‐mediated self‐association of the enzyme in vivo. We conclude, on the contrary, that the transhydrogenase octamer is partly immobilized in vivo by divalent‐cation‐mediated interactions with cell constituents (e.g. nucleic acids) preventing its self‐association.
The reduction of NAD+ by NADPH catalyzed by cell‐free extract transhydrogenase is not influenced by phosphate ions, while the reverse reaction is completely inhibited by 5 mM phosphate. This inhibition is released by adding excess divalent cations (10 mM CaCl2 or MgCl2). Since other metabolites (adenosine, 5′AMP, ADP, ATP) inhibit both activities more or less to the same extent it follows that the antagonistic action of phosphate and divalent cations is of primary importance in regulating the direction of intracellular transhydrogenation in A. vinelandii.
The existence of binding sites for these ions on the transhydrogenase subunit is indicated by studies on the inhibition of cell‐free extract transhydrogenase with the divalent thiol reagent p‐aminophenylarsenoxide. The rate of reaction is slowed down by magnesium and accelerated by phosphate ions.
Uptake of Iron from Transferrin by Isolated Rat‐Liver Mitochondria Mediated by Phosphate Compounds
Authors: KONOPKA Krystyna , ROMSLO Inge 
Published: July 2010

Isolated rat‐liver mitochondria accumulate iron from transferrin at neutral pH by a mechanism which is markedly stimulated by small‐molecular‐weight polyphosphate compounds. The efficiency of the phosphate compounds decreases in the order: pyrophosphate > ATP > GTP > 2,3‐bis‐(phospho)glycerate > phosphate.
The uptake has a very low energy dependence, and it does not depend on the hydrolysis of ATP or the saturation of transferrin, but it increases in parallel to the concentration of iron to reach a saturation level of 800–1200 pmol iron/mg protein.
Following a chase with unlabelled transferrin, (125I)‐labelled transferrin bound to the mitochondria remains constant, whereas the progressive uptake of 59Fe levels off.
During reincubation of iron‐loaded mitochondria up to 30% of the iron is mobilized in the presence of ascorbate and ATP (or apotransferrin).
The results suggest that iron is mobilized from transferrin by the polyphosphate compounds outside the mitochondria and taken up by the mitochondria in a subsequent reaction.
Cytochromes c‐556 from Three Genetic Races of Agrobacterium
Authors: VAN BEEUMEN Jozef , VAN DEN BRANDEN Christiane , TEMPST Paul , DE LEY Jozef 
Published: July 2010

The soluble cytochromes c‐556 from three strains of Agrobacterium tumefaciens, B6, II Chrys and Apple 185 have been purified to homogeneity. The strains are representative members of the three main genetic races of Agrobacterium. The purity of the final preparations was established by electrophoresis with an without sodium dodecyl sulphate, by analytical isoelectric focusing and ultracentrifugation, and by N‐terminal analysis.
Properties of these cytochromes were compared with those of cytochrome c‐556 from A. tumefaciens, strain B2a, a member of the same genetic race as strain B6. The four cytochromes are monohaem proteins with molecular weights of about 12300 (determined by four different methods). The isoelectric points of those from strains B6 and B2a are identical at pH 5.5, but they differ from the cytochromes of the other genetic races: cytochrome c‐556 from strain Apple 185 is more acidic (pH 5.2) and that from strain II Chrys more basic (pH 6.2). The cytochromes from strains B6 and B2a have very similar but not identical amino acid compositions; both of them differ more from Apple 185 than from II Chrys c‐556.
Comparison of the tryptic, chymotryptic and thermolytic fingerprints of cytochrome c‐556 from strains B2a and II Chrys reveals strong homology between the primary structures of these cytochromes. Therefore and because of the sequence identity of the first eight residues, the cytochromes c‐556 from strains II Chrys, B6 and B2a are most likely C‐terminal haem‐bound, of the same type as the cytochrome c′ from photosynthetic bacteria.
Purification and Subunit Structure of Rat‐Liver Phosphoprotein Phosphatase whose Molecular Weight is 260000 by Gel Filtration (Phosphatase IB)
Authors: TAMURA Shinri , TSUIKI Shigeru 
Published: July 2010

Phosphoprotein phosphatase IB is a form of rat liver phosphoprotein phosphatase, distinguished from the previously studied phosphoprotein phosphatase II [Tamara et al. (1980) Eur. J. Biochem. 104, 347–355] by earlier elution from DEAE‐cellulose, by higher molecular weight on gel filtration (260000) and by lower activity toward phosphorylase a. This enzyme was purified to apparent homogeneity by chromatography on DEAE‐cellulose, aminohexyl—Sepharose‐4B, histone‐Sepharose‐4B, protamine‐Sepharose‐4B and Sephadex G‐200.
The molecular weight of purified phosphatase IB was 260000 by gel filtration and 185000 from s 20° C, and Stokes' radius. Using historic phosphatase activity as the reference for comparison, the phosphorylase phosphatase activity of purified phosphatase IB was only one‐fifth that of phosphatase II.
Sodium dodecyl sulfate gel electrophoresis revealed that phosphatase IB contains three types of subunit, namely α, β and γ, whose molecular weights are 35000, 69000 and 58000, respectively. The α subunit is identical to the α subunit α phosphatase II. While the β subunit is also identical or similar to the β subunit of phosphatase II, the γ subunit appears to be unique to phosphatase IB.
When purified phosphatase IB was treated with 2‐mercaptoethanol at –20° C, the enzyme was dissociated to release the catalytically active α subunit. Along with this dissociation, there was a 7.4‐fold increase in phosphorylase phosphatase activity; but historic phosphatase activity increased only 1.6‐fold. The possible functions of the γ subunit are discussed in relation to this activation of enzyme.