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Query: UNIPROT:Q07644 (polypeptide)
 72,197 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The complete amino-acid sequence of Cu-Zn superoxide dismutase from white cabbage (Brassica oleracea) is reported. The polypeptide chain consists of 151 amino acids and has a molecular mass of 15,604 Da. The primary structure of the reduced and S-carboxymethylated protein was determined by automated solid phase sequence analysis of tryptic fragments and peptides obtained by digestion with Staphylococcus aureus proteinase V8. The protein shows a free amino terminus as was found for all non-mammalian Cu-Zn enzymes so far sequenced. Comparison of the amino-acid sequence from the plant Cu-Zn enzyme with those from nine eukaryotic enzymes reveals a high degree of homology (50-64%) among these enzymes. As already described for all the eukaryotic Cu-Zn superoxide dismutases also the plant enzyme shows a low homology (about 28%) with the bacteriocuprein of Photobacterium leiognathi. However, the amino-acid residues involved in metal binding, the half-cystine residues forming the intermolecular disulfide bridge, one of the arginine and some glycine and proline residues are conserved in all eleven Cu-Zn superoxide dismutases. Although the precise role of the 23 completely conserved residues is not yet completely understood, they appear to almost define the minimum structural requirements for optimizing the superoxide dismutation at the catalytic site, since functional differences between the eleven enzymes are not detectable.
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PMID:Primary structure of Cu-Zn superoxide dismutase of Brassica oleracea proves homology with corresponding enzymes of animals, fungi and prokaryotes. 379 Feb 49

We have explored a comprehensive experimental approach to determine whether the two condensing-enzyme active centers of the mammalian fatty acid synthetase are simultaneously functional. Our strategy involved utilization of trypsinized fatty acid synthetase, which is a nicked homodimer composed of two pairs of 125 + 95-kDa polypeptides. These core polypeptides lack the chain-terminating thioesterase domains but retain all other functional domains of the native enzyme and can assemble long-chain acyl moieties at a rate equal to that of the native enzyme. The 4'-phosphopantetheine content of these enzyme preparations, estimated from the amount of beta-alanine present, from the amount of taurine formed by performic acid oxidation and from the amount of carboxymethylcysteamine formed by alkylation with iodo[2-14C]acetate, was typically 0.86 mol/mol 95-kDa polypeptide. The stoichiometry of long-chain acyl-enzyme synthesis, measured with radiolabeled precursors, indicated that 0.84 mol acyl-chains were assembled/mol 95-kDa polypeptide. When the small amount of apoenzyme present is taken into account, this stoichiometry translates to 1.94 acyl chains per holoenzyme dimer. The 125-kDa polypeptide of one subunit could be cross-linked to the 95-kDa polypeptide of the other subunit by 1,3-dibromo-2-propanone yielding a single molecular species of 220 kDa. Cross-linking was accompanied by a loss of condensing-enzyme activity. This result is consistent with a structurally symmetrical model for the animal fatty acid synthetase [J.K. Stoops and S.J. Wakil (1981) J. Biol. Chem. 256, 5128-5133] in which the juxtaposed 4'-phosphopantetheine and cysteine thiols of opposing subunits that form the two potential catalytic centers for condensing activity are readily susceptible to cross-linking. Both half-maximal cross-linking and 50% inhibition of activity were observed with 1 mol 1,3-dibromo-2-propanone bound/mol enzyme. After assembly of long-chain acyl moieties on the 4'-phosphopantetheine residues, no vacant condensing-enzyme active sites were demonstrable either by cross-linking with 1,3-dibromo-2-propanone or by formation of carboxymethylcysteamine on treatment with iodoacetate. These results are consistent with a structurally and functionally symmetrical model for the mammalian fatty acid synthetase in which the two condensation sites are simultaneously active.
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PMID:Mammalian fatty acid synthetase is a structurally and functionally symmetrical dimer. 384 Apr 36

We have constructed a nearly full length cDNA clone, pGTA/C44, complementary to the rat liver glutathione S-transferase Yb1 mRNA. The nucleotide sequence of pGTA/C44 has been determined, and the complete amino acid sequence of the Yb1 subunit has been deduced. The cDNA clone contains an open reading frame of 654 nucleotides encoding a polypeptide comprising 218 amino acids with Mr = 25,919. The NH2-terminal sequence deduced from DNA sequence analysis of pGTA/C44 is in agreement with the first 19 amino acids determined for purified glutathione S-transferase A, a Yb1 homodimer, by Frey et al. (Frey, A. B., Friedberg, T., Oesch, F., and Kreibich, G. (1983) J. Biol. Chem. 258, 11321-11325). The DNA sequence of pGTA/C44 shares significant sequence homology with a cDNA clone, pGT55, which is complementary to a mouse liver glutathione S-transferase (Pearson, W. R., Windle, J. J., Morrow, J. F., Benson, A. M., and Talalay, P. (1983) J. Biol. Chem. 258, 2052-2062). We have also determined 37 nucleotides of the 5'-untranslated region and 348 nucleotides of the 3'-untranslated region of the Yb1 mRNA. The Yb1 mRNA and subunit do not share any sequence homology with the rat liver glutathione S-transferase Ya or Yc mRNAs or their corresponding subunits. These data provide the first direct evidence that the Yb1 subunit is derived from a gene or gene family which is distinct from the Ya-Yc gene family.
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PMID:Rat liver glutathione S-transferases. Nucleotide sequence analysis of a Yb1 cDNA clone and prediction of the complete amino acid sequence of the Yb1 subunit. 384 Apr 77

Light-mediated conformational changes in highly purified 124-kDa phytochrome preparations from etiolated oat seedlings have been identified by steric exclusion high performance liquid chromatography and limited proteolytic studies. Steric exclusion high performance liquid chromatography studies of oat and rye phytochromes show photoreversible changes in retention times, with the red absorbing form of phytochrome (Pr form) eluting later than the far red absorbing form of phytochrome produced by saturating red light illumination of Pr (Pfr form) in a variety of different mobile phase buffers. Molecular mass calibration with globular protein standards in Tris-glycol buffers provides estimates of 318-349 and 363-366 kDa for the molecular sizes of the Pr and Pfr forms, respectively. These analyses support earlier studies that phytochrome is a nonglobular homodimer of 124-kDa subunits in vitro. Limited proteolytic dissection of phytochrome in nondenaturing buffers with seven different endoproteases provides evidence for two "operational" domains within the 124-kDa subunit with molecular mass values of 69-72 and 52-55 kDa. The larger 69-72-kDa domain contains the site for the chromophore attachment as shown by gel electrophoresis derived enzyme-linked immunosorbent assay utilizing site-directed rabbit antiserum to a synthetic undecapeptide which is homologous with the chromophore binding site on oat phytochrome. This chromophore domain exhibits a compact structure, resistant to further proteolysis except near its N terminus. By contrast, the 52-55-kDa nonchromophore domain contains multiple sites for further proteolytic cleavage as revealed by rapid cleavage to smaller polypeptide fragments. Detailed kinetic analyses of the limited proteolytic cleavage of phytochrome with four endoproteases, subtilisin BPN', thermolysin, trypsin, and clostripain, has mapped specific regions within the 124-kDa subunit that participate in light-induced conformational changes. These include a 4-10-kDa region near the N terminus of the chromophore binding domain and at least two regions within the nonchromophore domain. A comprehensive peptide map of the oat phytochrome subunit is presented, which incorporates the results of these proteolytic studies with the recent, yet unpublished sequence analyses of Avena phytochrome cDNA clones which show the N-terminal localization of the chromophore binding site (Hershey, H. P., Colbert, J. T., Lissemore, J. L., Barker, R. F., and Quail, P. H. (1984) Proc. Natl. Acad. Sci. U.S.A. 81, 2332-2336).
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PMID:Structure function studies on phytochrome. Identification of light-induced conformational changes in 124-kDa Avena phytochrome in vitro. 388 93

In Klebsiella pneumoniae, the nifH gene encodes the Fe protein (Kp2) polypeptide that is assembled into a homodimer responsible for the reduction of nitrogenase. Escherichia coli or the yeast Saccharomyces cerevisiae, transformed with the K. pneumoniae nifH gene in suitable expression vectors, synthesize the Fe protein polypeptide. This study examines the assembly of the nifH gene product into its characteristic dimeric structure in E. coli and in yeast. Immunoblotting methods, as well as 55Fe2- labeling of K. pneumoniae were employed to detect native nitrogenase components in cell lysates. E. coli and yeast transformants contained a protein similar to native Kp2 in its immunoreactivity, apparent molecular weight, and lability in the presence of oxygen or MgATP. While in E. coli the co-introduction of nifH and nifM resulted in enhanced levels of the nifH product, it appears that the nifH gene product alone is sufficient for the assembly of an Fe protein-like structure in foreign prokaryotic and eukaryotic hosts.
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PMID:Expression of nitrogen fixation genes in foreign hosts. Assembly of nitrogenase Fe protein in Escherichia coli and in yeast. 388 51

The hemoglobin found in the nucleated erythrocytes of the arcid blood clam Noetia ponderosa is heterogeneous and consists of two electrophoretic components, Hb-Major and Hb-Minor, present in about 80% and 20% proportions, respectively. Both components are hemoglobin dimers over a wide concentration range based on light-scattering measurements. No higher aggregation states are observed. The oxygen binding by Hb-Major and Hb-Minor is characterized by p50 values of 16.8 and 8.7 mm of Hg and Hill coefficients of 1.4 and 1.2, respectively, at pH 7.0 and 25 degrees C. Neither component exhibits an alkaline Bohr effect. An unusual nonlinear Hill plot is observed for Hb-Major. Hb-Major is composed of two different polypeptide chains and thus is a heterodimer based on sodium dodecyl sulfate/urea-polyacrylamide gel electrophoresis and reverse phase high performance liquid chromatography. By the same methods, Hb-Minor is a homodimer and may share a common chain with Hb-Major. Amino acid compositions of the two hemoglobins indicate 2 histidines/polypeptide chain which are presumably involved in the coordination of the heme iron. Visible absorption spectra indicate the heme environment is normal in the oxy state but perhaps more constrained in the deoxy state. Oxygen binding as a function of temperature and concentration and binding by the intact erythrocytes indicates the absence of intracellular regulators of oxygen binding.
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PMID:Dimeric hemoglobins from the arcid blood clam, Noetia ponderosa. Structure and functional properties. 398 Apr 79

Calmodulin-dependent cyclic nucleotide phosphodiesterase from bovine brain is found to be composed of two distinct subunits, 60,000- and 63,000-dalton polypeptides. Peptide mapping of the subunits by partial proteolysis demonstrated that the 60-kDa polypeptide is not derived from the 63-kDa species. The interaction of the enzyme with three monoclonal antibodies, A6, C1, and A2, and the analysis of immunocomplexes by sucrose density gradient centrifugation revealed that calmodulin-dependent cyclic nucleotide phosphodiesterase exists in three different forms, i.e. (a) homodiamer of 60-kDa, (b) heterodimer of 60- and 63-kDa, and (c) homodimer of 63-kDa. A6 antibody reacts with both 60- and 63-kDa polypeptides indicating that they are immunologically related. C1 and A2 antibodies react with only 60-kDa polypeptide species. By using C1 Sepharose 4B affinity column chromatography, the 63-kDa homodimer which did not bind to the column (Fraction I) was separated from the 60-kDa polypeptide containing isozymes (the heterodimer and the 60-kDa homodimer) which were retained on the column and later eluted as a mixture (Fraction II). Fraction I, the 63-kDa homodimer enzyme, has higher Vmax toward cGMP as substrate than cAMP whereas the opposite was found with Fraction II. The specific activity of Fraction II enzyme toward cAMP was approximately 500 mumol/min/mg, the highest value ever reported for brain calmodulin-dependent cyclic nucleotide phosphodiesterase preparations.
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PMID:Demonstration of bovine brain calmodulin-dependent cyclic nucleotide phosphodiesterase isozymes by monoclonal antibodies. 608 30

The functional unit of arom polyenzyme conjugate of Neurospora crassa was determined by analysis of radiation inactivation of each of the five activities in the conjugate. The functional targets for all five enzymes were in close agreement with the value of 300,000 obtained by conventional hydrodynamic procedure for the native dimeric structure. These data indicate that at least 95% of the functional enzyme system in crude extracts exists in a dimeric form and that both polypeptide chains of the homodimer are required for full activity of each of the five enzymes.
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PMID:The functional unit of the arom conjugate in Neurospora. 621 84

The surface proteins of lymphocytes from spleen and thymus and several cultured lymphoid tumor lines were radioiodinated in situ, solubilized with Triton X-100, and examined for the presence of disulfide-bonded subunits by two-dimensional (intact, reduced) NaDodSO4/polyacrylamide gel electrophoresis. [Hynes, R. O. & Destree, A. (1977) Proc. Natl. Acad. Sci. USA 74, 2855-2859]. Few lymphocyte surface proteins were found to consist of disulfide-bonded subunits, and the most prominent of these could be identified. In normal B lymphocytes and B-lymphoma cells, IgD or IgM (or both) were the major disulfide-bonded proteins, and these were easily detectable, even without immunoprecipitation. In contrast, analysis of thymocytes and T-lymphoma cells did not reveal any protein resembling immunoglobulin in its chain structure. The major labeled thymocyte membrane protein consisting of disulfide-bonded subunits was identified as the Ly-2/3 antigen. It appeared to contain disulfide-bonded homodimers of Mr 35,000 (alpha 2) noncovalently associated with a second pair of homodimers of Mr 30,000 (beta 2). Peptide mapping showed these polypeptides to be homologous. A third disulfide-bonded homodimer, which was heterogeneous in apparent Mr, appeared to be part of the Ly-2/3 complex. All cultured T- and B-lymphoma lines examined were found to possess a major surface protein that appeared to be a disulfide-bonded homodimer of a polypeptide of Mr 95,000. This protein was identified as the receptor for transferrin. It is suggested that the presence of two or more subunits in cell surface receptors renders their ligand functionally bivalent, making ligand-induced receptor aggregation possible.
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PMID:Subunit structure of cell surface proteins: disulfide bonding in antigen receptors, Ly-2/3 antigens, and transferrin receptors of murine T and B lymphocytes. 627 Jun 81

A type II DNA topoisomerase has been purified from the nuclei of Drosophila melanogaster 6- to 18-h-old embryos. The enzyme, as assayed by its ability to catenate supercoiled DNA, behaved as a single homogeneous species throughout the procedure and the yield was approximately 0.5 mg of protein/100 g of dechorionated embryos. The final product was entirely ATP-dependent and free of topoisomerase I, endonuclease and protease activities. The purified topoisomerase II had a Stokes radius of 69 A and a sedimentation coefficient (S20,w) of 9.2 S, leading to a calculated native molecular weight of approximately 261,000. The protein consists of a single polypeptide of molecular weight 166,000, as determined by electrophoresis on sodium dodecyl sulfate-polyacrylamide gels. Taken together with the above hydrodynamic studies, the Drosophila enzyme is probably a homodimer, as has been observed for other eukaryotic type II enzymes. Thus, it appears that during the course of evolution the heterologous subunits which comprise bacterial type II topoisomerases have been combined into a single polypeptide chain in eukaryotes.
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PMID:DNA topoisomerase II from Drosophila melanogaster. Purification and physical characterization. 630 10


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