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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Structural similarities between proteins with no amino acid sequence homology either indicate a phylogenetic relationship, or they are merely the expression of a physically preferred way of folding a polypeptide chain. It is shown that one can distinguish between these alternatives by evaluating the "significance of the similarity". Such significances have been derived for comparison between chain folds containing beta-pleated sheets (Schulz and Schirmer, 1974; Richardson et al., 1976; Sternberg and Thornton, 1976). An extension of this method to comparisons between any two chain folds is outlined here.
J Mol Evol 1977 Aug 05
PMID:Recognition of phylogenetic relationships from polypeptide chain fold similarities. 89 34

The A-protein of coliphage MS2 was purified to a state of sufficient homogeneity to study its primary structure. The NH2-terminal sequence was determined for the first 8 residues. Comparison with the reported sequence of R17 protein (Weiner, A. M., Platt, T., and Weber, K. (1972) J. Biol. Chem. 247, 3242-3251) shows a difference at position 6 where alanine in R17 is replaced by threonine in MS2. The COOH-terminal sequence was shown to be -Arg-Leu-Ser-Arg, confirming the existence of UAG as the termination codon of the maturation protein (Comtreras, R., Ysebaert, M., Min Jou, W., and Fiers, W. (19731 Nature New Biol. 241, 99-101; Vandekerckhove, J., Nolf, F., and Van Montagu, M. C. (1973) Nature New Biol. 241, 102; Remaut E., and Fiers, W. (1972) J. Mol. Biol. 71, 243-261). Peptides obtained by enzymatic hydrolysis with trypsin were fractionated by a combination of gel filtration and paper electrophoresis and chromatography. Thirty-eight peptides were analyzed for amino acid composition and sequence. They provide information for 312 of the 393 residues of the A-protein polypeptide chain.
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PMID:Sequence of the A-protein of coliphage MS2. I. Isolation of A-protein, determination of the NH2- and COOH-terminal sequences, isolation and amino acid sequence of the tryptic peptides. 91 36

alpha-Hemocyanin from the Roman snail Helix pomatia is composed of polypeptide chains with a molecular weight of 360000 +/- 30000. The cylindrically shaped hemocyanin molecule contains 20 of these large chains. The polypeptide chain has been split into components with molecular weights of: 210000, 154000, 147000, 112000, 120000, 98000, 55000, and 50000, by gentle proteolysis with enzymes of different specificities. Most of the fragments have molecular weights which are about 50000 or a multiple of 50000. Departure from these values, as found in the 112000 and 120000 fragments, is probably caused by the high carbohydrates content of these components. A mixture of these fragments has the same oxygen binding properties as the nondigested protein. Subtilisin converts the hemocyanin polypeptide chain, under appropriate conditions, almost completely into fragments of 50000 and 55000 daltons with conservation of the oxygen binding properties of the nondigested protein. We conclude from these studies that the polypeptide chain of Helix pomatia alpha-hemocyanin is folded into about seven compact tertiary structures, which are covalently interconnected. This chain of structural domains has been visualized. (Siezen and Van Bruggen (1974), J. Mol. Biol. 90, 77-89) by electron microscopy, which shows 1/20 hemocyanin molecules to be flexible structures consisting of 7-8 apparently spherical units of 55-60 A diameter.
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PMID:Proteolytic fragmentation of Helix pomatia alpha-hemocyanin: structural domains in the polypeptide chain. 93 32

The methods of Chou & Fasman [Biochemistry (1974) 13, 211-222, 222-245] and of Lim [J. Mol. Biol. (1974)88, 857-872, 873-894] for predicting secondary structure from amino acid sequence have been applied to five predominantly helical membrane-associated peptides. The predictions from the method of Lim (1974a,b) are consistent with the experimental observations, whereas those from Chou & Fasman (1974a,b), although not inconsistent with alpha-helix, favour a beta-structure for several very hydrophobic regions. The results may be rationalized in terms of the effect of the solvent on the conformation of a polypeptide.
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PMID:The prediction of the conformation of membrane proteins from the sequence of amino acids. 94 84

We find that specific oxidation for the Met-192 residue in delta-chymotrypsin to methionine sulfoxide results in a twofold increase in Km(app) and unchanged kcat in the hydrolysis of N-acetyl mono(amino acid) amide substrates. However, the catalyzed hydrolyses of N-acetyl dipeptide amide substrates by (methionine sulfoxide)-192-delta-chymotrypsin (MS-delta-Cht) shows a four- to fivefold decrease in kcat and unchanged Km(app) with respect to delta-chymotrypsin. Hydrolysis of alpha-casein by MS-delta-Cht shows a similar 4.2-fold decrease in kcat. These results imply that the Met-192 acts differently with substrates that bind only in the primary, S1, binding site (i.e., AcPheNH2) from those that bind to more extended regions of the enzyme active site. In the binding of c+AcPheNH2 and AcTrpNH2, the results support a mechanism in which the Met-192 acts to slow the rate of sustrate dissociation from the Michaelis complex to free substrate and enzyme. This is in agreement with the x-ray crystallographic structure of dioxane inhibited alpha-chymotrypsin (Steitz, T., et al. (1969), J. Mol. Biol. 46, 337). However, this mechanism is not apparent when peptide and protein substrates bind. The decrease in kcat on Met-192 modification of approximately fivefold in the hydrolysis of polypeptide substrates show a small, but significant, catalytic contribution of the Met-192 toward the lowering of the energy of activation polypeptide substrate hydrolysis by chymotrypsin. This may support the crystallographic model of Fersht et al. (Fersht, A., et al. (1973), Biochemistry 12, 2035) in which it is proposed that the Met-192 participates in the distortion of bound polypeptide substrates toward the reaction transition-state configuration and, thus, plays a role in catalysis. However, if this mechanism occurs, the effect is small, only contributing about 1 kcal/mol to the lowering of the reaction activation energy.
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PMID:The role of methionine-192 of the chymotrypsin active site in the binding and catalysis of mono(amino acid) and peptide substrates. 96 30

The assignment of the known ade genes to steps in purine biosynthesis in Schizosaccharomyces pombe has been completed with the demonstration that an ade3 mutants lacks FGAR amidotransferase, ade1A mutants lack GAR synthetase and ade1B mutants lack AIR synthetase. A comparison of enzyme activity with map position for ade1 mutants shows that (1) complementing ade1A mutants lack GAR synthetase but posses wild type amounts of AIR synthetase, (2) complementing ade1B mutants lack AIR synthetase but posses variable amounts of GAR synthetase, (3) non-complementing mutants lack both activities. In wild type strains the two activities fractionate together throughout a hundred-fold purification. Hence the ade1 gene appears to code for a bifunctional enzyme catalysing two distinct steps in purine biosynthesis. The two activities are catalysed by two different regions of the polypeptide chain which can be altered independently by mutation. Gel filtration studies on partially purified enzymes from wild type and various complementing mutant strains, indicate that the bifunctional enzyme is a multimer consisting of between four and six sub-units of 40,000 daltons each. GAR synthetase activity is associated with both the monomeric and multimeric forms but AIR synthetase is only associated with the multimer. A comparison of enzyme levels between diploids and their original complementing haploid strains suggests that complementation is due to hybrid enzyme formation.
Mol Gen Genet 1976 Sep 23
PMID:The product of the ade1: gene in Schizosaccharomyces pombe: a bifunctional enzyme catalysing two distinct steps in purine biosynthesis. 96 58

A rapid method suitable for purifying large amounts of mitochondria from rat liver using isopycnic zonal centrifugation is described. The RNA polymerase isolated from the purified mitochrondria was found associated with one peak when resolved by DEAE Sephadex chromatography. The enzyme was next fractionated on a phosphocellulose column followed by glycerol gradient centrifugation. A 600-fold purification was achieved when the enzyme was finally filtered through agarose gel. This final enzyme fraction consisted of one polypeptide chain as shown by polyacrylamide gel electrophoresis profiles. The enzyme has a greater preference for poly [d(A-T)] templates than for rat liver mitochondrial DNA. Inhibition of the enzyme activity required high concentrations of the inhibitors. The resistance of the enzyme to alpha-amanitin indicated that there was no contamination from nuclear RNA polymerase II. The conclusion is drawn that the mitochondrial RAN polymerase activity is associated with a single polypeptide.
Mol Cell Biochem 1976 Dec 10
PMID:Some properties of rat liver mitochondrial RNA polymerase. 100 1

The kinetics of nitration of tyrosine residues in histones F1 and F2a1 by tetranitromethane has been investigated. At low ionic strength and 30-fold molar excess of nitrating agent the nitration reaction results in fast modification of all tyrosine residues in both histones. At the same time the rates of modification of different tyrosine residues in histone F2a1 are not identical and markedly exceed the rate of N-Ac-OEt-Tyr nitration in a model system. The increase of reaction mixture ionic strength causes an increase of modification rates. The differential UV-absorption spectra of histone F1 obtained by temperature perturbation show an abnormal positive characteristic maximum at 286.8 nm. Analysis of the dependence of nitration rates of tyrosine residues in histones in saline solutions upon the ionic strength and of difference UV-absorption spectra of histones leads to a conclusion that there are specific interactions of definite parts of histone polypeptide chains. These interactions may arise from aggregation of histone molecules.
Mol Biol (Mosk)
PMID:[Tyrosine residues in histones. Kinetics of histones F1 and F2A1 nitration by tetranitromethane]. 105 46

Microsomes isolated from the fibroin region of the Bombyx mori silkgland synthesize in the cell-free system a glycin rich polypeptide or polypeptides presumably representing fibroin precursors. Besides microsomes the system requires ATP and ATP-generating system, GTP, soluble protein fraction and tRNA, glycine incorporation is inhibited by puromycin and cycloheximide. It is shown that the synthesis of a polypeptide with high Gly/Lys ratio requires soluble protein fraction isolated from the silk gland at the end of the instar V. When the soluble protein fraction from the larvoe at the early instar V is used the Gly/Lys ratio in the product is markedly lower. These results permit to suggest that fibroin synthesis may be regulated at the level of tRNA aminoacylation.
Mol Biol (Mosk)
PMID:[Properties of the cell-free protein synthesizing system from the fibroin region of the Bombyx mori silkgland]. 105 90

The conformational changes in aspartate transcarbamylase upon binding of substrates or regulatory ligands and the effects of alterations in the subunit structure on the allosteric interactions are reviewed. The available information including recent results from studies of the c3r6 complex (c denotes the catalytic polypeptide and r, the regulatory polypeptide) is considered in terms of the existing models for the discrepancies between experimental observations and the present models could be resolved by postulating an important role for r:r interactions in the allosteric mechanism. A new model is presented in which an obligatory conformational change upon binding of substrates results in an alteration in the relative orientation of c versus r. As a consequence of symmetry conservation, the r:r domain is shifted to a position of higher potential energy. By favoring one or the other alternative r:r domains, CTP and ATP can respectively enhance and reduce the sigmoidal character of substrate saturation. The model is shown to be consistent with all of the important known properties of the enzyme. Because the heterotropic effects of CTP or ATP are postulated to operate via a mechanism separate from that for the homotropic effects of the substrates, this model accounts satisfactorily for the observation by Kerbiriou and Herve (Kerbiriou, D., and Herve, G. (1973) J. Mol. Biol. 78, 687-702) that homotropic effects can be abolished whereas heterotropic effects are retained in the altered enzyme from Escherichia coli grown in the presence of 2-thiouracil.
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PMID:Subunit interactions in aspartate transcarbamylase. A model for the allosteric mechanism. 108 47


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