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T C Stadtman

Publications and source records attributed to T C Stadtman.

At least 127 records · Page 7Linked to original sources
PubMed1972

Clostridium barkeri sp. n.

Clostridium barkeri sp. n. has been described, and its relationship to other clostridia is discussed.

Acetates↗
PubMed1971

Vitamin B 12.

In spite of the considerable progress made in recent years toward the understanding of the chemistry and biological function of the cobalt-containing B(12) group of compounds, much of the information still is more descriptive than definitive in nature. In general terms, it is known that the free vitamin forms can function as methyl group carriers and that the 5'-deoxyadenosyl or coenzyme forms serve as hydrogen carriers; but the mechanism of these processes is not understood in detail. More systematic studies of the pure chemistry of these complex molecules containing a carbon-cobalt covalent bond are needed before the biochemist can interpret many of his observations on the enzyme-catalyzed reactions. Even in relatively simple solutions it is difficult to ascertain the state of oxidation of several of the vitamin forms, and these problems are compounded when the reactive thiol compounds and complex proteins of the biological systems also are present. For example, both vitamin B(12r) (the Co(2+) form) and corresponding analogs are known to disproportionate in solution to B(12s) (Co(1+)) and B(12a) (Co(3+)) under a variety of mild conditions (12, 57). This means that in the biological systems it is exceedingly difficult to ascertain the chemical nature of many B(12) intermediates and reaction products. The role of the protein moiety of the various B(12)-linked enzymes in the catalytic processes is little known as is, also, the mode of binding of the B(12) derivative to the protein. These types of questions perhaps can be answered eventually by the crystallographers, whose art is becoming increasingly sophisticated. Note added after preparation of manuscript. In contrast to the values given in Table 4 for the molecular weights of the two dissimilar protein moieties of glycerol dehydrase, a recent report (57a), gives a value of 188,000 for the molecular weight of a stable, catalytically inactive complex of 1 mole of hydroxocobalamin and 1 mole of the apoenzyme complex of glycerol dehydrase. The latter is presumed to contain one equivalent of each of the two dissimilar protein subunits. The original estimate of 240,000 as the molecular weight of the unstable sulfhydryl protein moiety (39) was undoubtedly made on partially aggregated material.

Adenosine Triphosphate↗
PubMed1970

Nicotinic acid metabolism. V. A cobamide coenzyme-dependent conversion of alpha-methyleneglutaric acid to dimethylmaleic acid.

A new B(12)-coenzyme-dependent isomerization, catalyzed by extracts of a nicotinate-fermenting clostridium, results in the conversion of alpha-methyleneglutaric acid to dimethylmaleic acid. These two acids are intermediates in the multistep anaerobic process wherein nicotinate is converted, ultimately, to one mole each of propionate, acetate, carbon dioxide, and ammonia. Dimethylmaleic acid reacts in its anhydride form with 2,4-dinitrophenylhydrazine to form N-2',4'-dinitrophenyl-anilino-3,4-dimethylmaleimide. The characteristic reddish color exhibited by the latter derivative in alkaline solution serves as a convenient quantitative assay for dimethylmaleic acid. Comparison of the 2,4-dinitrophenylhydrazine derivatives of the product of the enzymic reaction and of synthetic dimethylmaleic anhydride showed them to be identical in every respect.

Acetates↗
PubMed1970

Small Colonies of Clostridium sticklandii Resulting from Nitrosoguanidine Treatment and Exhibiting Defects in Catabolic Enzymes.

Several strains of Clostridium sticklandii, isolated from small colonies arising after treatment with 1-methyl-3-nitro-1-nitrosoguanidine, exhibited markedly depressed activities of certain catabolic enzyme systems known to provide energy to the organism in the form of adenosine triphosphate. In some of these strains the levels of glycine reductase, the ability to ferment lysine to fatty acids and ammonia, and formate-dependent 2,3-5-triphenyltetrazolium chloride reduction were only 0 to 10% of that of the wild type. Another subgroup of mutants exhibited activities of some of these enzymes from 1.3 to 3 times higher than those of the wild type. Small-colony mutants of an obligate anaerobe, like those of oxygen-utilizing organisms, can therefore be due to defects in one or more of their energy-providing systems. The merits of small-colony formation as an auxiliary marker for the isolation of catabolic mutants are discussed.

Journal Article↗