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PubMed1985

Isolation and characterization of DL-methylmalonyl-coenzyme A racemase from rat liver.

Certain amino acids and other compounds are metabolized via propionyl-CoA----D-methylmalonyl-CoA----L-methylmalonyl- CoA----succinyl-CoA----tricarboxylic acid cycle. D-Methylmalonyl-CoA can also be converted to methylmalonic acid and coenzyme A by a specific hydrolase that does not act on L-methylmalonyl-CoA [R.J. Kovachy, S.D. Copley, and R.H. Allen (1983) J. Biol. Chem. 258, 11415-11421]. Because little is known about mammalian DL-methylmalonyl-CoA racemase and because it is involved in the flow of D-methylmalonyl-CoA to L-methylmalonyl-CoA----tricarboxylic acid cycle (versus to methylmalonic acid), we developed a new assay and purified rat liver racemase 23,000-fold to homogeneity. The molecular weight of the racemase is 32,000 and it contains two subunits of Mr 16,000 that are not connected by disulfide bonds. The rat liver and the rat and human white blood cell racemase are immunologically related. They are completely inactivated by EDTA and can be activated by the addition of Co+2, with 50% activation occurring at a concentration of 0.2 microM. Lower levels for maximal activation were obtained with higher concentrations of Co+3, Fe+2, and Mn+2. Other metals such as Zn+2, Cu+2, Cu+1, and Cd+2 completely inhibited racemase even in the presence of equal concentrations of Co+2. The purified racemase appears to bind 1 mol Co/mol subunit.

Amino Acids↗
PubMed1986

Isozymes of phosphoglyceromutase from the developing endosperm of Ricinus communis: isolation and kinetic properties.

The isozymes of phosphoglyceromutase from the developing endosperm of Ricinus communis have been partially purified. The purified cytosolic and plastid isozymes have specific activities of 622.8 and 83.8 mumol min-1 mg protein-1, respectively. They both have relative molecular masses of approximately 64,000. The cytosolic enzyme has lower Km values for both 2-phosphoglycerate and 3-phosphoglycerate than the plastid enzyme. The Km values for 3-phosphoglycerate are 330 +/- 25 and 430 +/- 48 microM for the cytosolic and plastid isozymes, respectively. The corresponding Km values for 2-phosphoglycerate are 60 +/- 10 and 112 +/- 22 microM. The two isozymes also have different pH optima and heat labilities. Neither isozyme requires 2,3-bisphosphoglycerate or a divalent cation and neither is regulated by metabolites.

Cytosol↗
PubMed1976

A study of phosphoglycerate kinase in human erythrocytes. I. Enzyme isolation, purification and assay.

The enzyme ATP-3-phospho-D-glycerate-1-phosphotransferase (EC 2.7.2.3) (phosphoglycerate kinase) has been isolated from human red cells in crystalline form by a modification of the method of Yoshida and Watanabe (1972) J. Biol. Chem. 247, 440-445). The crystalline enzyme was further purified by electrofocusing using carrier ampholytes (pH 7-9). The isoelectric point of phosphoglycerate kinase was estimated to be 8.75. The specific activity of purified phosphoglycerate kinase from electrofocusing was 2200 units per mg of protein at pH 8.3 (37 degrees C). Enzyme activity was assayed in the forward direction leading from 1,3-diphosphoglycerate to a 3-phosphoglycerate using a fluorimetric procedure for NAD-coupled enzymes for the measurement of the reaction rate at very low substrate concentrations. The auxiliary indicator enzymes were added in excess to yield true initial velocity kinetics, i.e. with no time lag upon addition of substrate (1,3-diphosphoglycerate). This was established theoretically using a mathematical model and confirmed experimentally. Further phosphoglycerate kinase was shown to be the rate-limiting step when the assay conditions were varied.

Adenosine Diphosphate↗
PubMed1979

Amino acid sequences of soluble tryptic peptides of chorismate mutase/prephenate dehydratase from Escherichia coli K12.

The amino acid sequences of 28 soluble tryptic peptides from chorismate mutase/prephenate dehydratase from Escherichia coli K12 have been determined. Together with the four unique cysteine-containing peptides sequenced by Gething and Davidson ((1976) Eur. J. Biochem. 71, 327-336) this accounts for approximately 75% of the total sequence expected for this protein. A high frequency of identify between some of the peptides suggests the possibility of gene duplication during the evolution of the structural gene for the enzyme.

Amino Acid Sequence↗
PubMed1984

Cell-free translation of messenger RNA for human bisphosphoglyceromutase.

mRNAs prepared from different human tissues were translated in a cell-free reticulocyte lysate system and, when present, the neosynthesized bisphosphoglyceromutase ( BPGM ) was specifically isolated by immunoprecipitation and analyzed by polyacrylamide gel electrophoresis. Analysis of the translation products showed that bisphosphoglyceromutase was synthesized in vitro with its mature molecular weight and messenger RNA specifying the synthesis of BPGM exhibited a sedimentation coefficient of 12 S in human reticulocytes. This synthesis seems to be highly tissue specific since we could not evidence any synthesis of this enzyme using mRNA obtained from non erythroid tissue. The BPGM synthesis represents 0.1% of the total neosynthesized non heme proteins in human reticulocyte and ten times less (0.01%) in human fetal liver.

Animals↗
PubMed1992

Glial cells as a model for the role of cobalamin in the nervous system: impaired synthesis of cobalamin coenzymes in cultured human astrocytes following short-term cobalamin-deprivation.

The conversion of cyanocobalamin to adenosyl- and methylcobalamin is impaired in cobalamin-deficient cultured human glial cells. In contrast cultured human skin fibroblasts retained their ability to synthesize coenzyme forms when grown in cobalamin-deficient medium. Cells were pre-conditioned by growing in cobalamin-deficient media for six weeks and then subcultured in medium containing either free or transcobalamin II-bound 57Co-cyanocobalamin. Although both coenzyme levels were low in cobalamin-deficient glial cells, the decrease in methylcobalamin was more marked than that of adenosylcobalamin. Methionine synthase and Cb1 reductase activities were markedly decreased in cobalamin-deficient glial cells but were unchanged in fibroblasts cultured in cobalamin-deficient medium. Our data suggest that in glial cells, cobalamin coenzyme synthesis and function is exquisitely sensitive to short-term cobalamin deprivation. Glial cells apparently synthesize and secrete transcobalamin II since antibodies directed against the transport protein inhibit the uptake of free cobalamin.

5-Methyltetrahydrofolate-Homocysteine S-Methyltran↗