A glyoxalase I inhibitor of a new structural type produced by Streptomyces

Many streptomyces strains produced an inhibitor of crude glyoxalase prepared from rat liver which did not inhibit glyoxalase I prepared from yeast. Another inhibitor, C11H14O6, which inhibited glyoxalases prepared from both rat liver and yeast was obtained from a cultured broth of Streptomyces griseosproeus and crystallized. Preincubation of this inhibitor with reuduced glutathione increased its inhibitory activity, which suggested its reaction with reduced glutathione. It showed a strong inhibition of growth of HeLa cells and inhibition of Ehrlich ascites carcinoma by daily injection. It also showed weak inhibition of the solid type of Ehrlich carcinoma and prolonged the survival period of mice inoculated with L-1210 cells.

Purification properties and subunit composition of pig heart lipoate acetyltransferase

Lipoate acetyltransferase [acetyl-CoA: dihydrolipoate S-acetyl-transferase, EC 2.3.1.12], the core enzyme of the pyruvate dehydrogenase complex, has been highly purified by gel chromatography on Sepharose 6B and sucrose density gradient centrifugation in the presence of potassium iodide. The native enzyme has a sedimentation coefficient (S020,W) of 26.7S and a diffusion coefficient (D020,W) of 1.25 x 10(-7) cm2.-sec-1. The weight-average molecular weight was estimated to be 1.8 million from the sedimentation equilibrium data. The content of right-handed alpha helix in the enzyme molecule was estimated to be about 25% by optical rotatory dispersion and about 22% from the circular dichroism spectra. The enzyme was found to contain about 23 moles of protein-bound lipoic acid per mole of enzyme; some other properties are also reported. Lipoate acetyltransferase dissociated to yield a single subunit with a molecular weight of 74,000 as estimated by polyacrylamide gel electrophoresis in sodium dodecyl sulfate and by gel filtration on Bio-Gel in 6 M guanidine-HCl. The molecular weight was also estimated to be 74,000 from sedimentation equilibrium data in 6 M guanidine-HCl] containing 0.1 M 2-mercaptoethanol. Evidence is presented that 1 molecule of lipoate acetyltransferase apparently consists of 24 very similar subunits, each of which contains NH2-terminal alanine. Each subunit contains 1 molecule of covalently bound lipoic acid.

A kinetic study of the alpha-keto acid dehydrogenase complexes from pig heart mitochondria

The kinetic mechanisms of the 2-oxoglutarate and pyruvate dehydrogenease complexes from pig heart mitochondria were studied at pH 7.5 and 25 degrees. A three-site ping-pong mechanism for the actin of both complexes was proposed on the basis of the parallel lines obtained when 1/v was plotted against 2-oxoglutarate or pyruvate concentration for various levels of CoA and a level of NAD+ near its Michaelis constant value. Rate equations were derived from the proposed mechanism. Michaelis constants for the reactants of the 2-oxoglutarate dehydrogenase complex reaction are: 2-oxoglutarate, 0.220 mM; CoA, 0.025 mM; NAD+, 0.050 mM. Those of the pyruvate dehydrogenase complex are: pyruvate, 0.015 mM; CoA, 0.021 mM; NAD+, 0.079 mM. Product inhibition studies showed that succinyl-CoA or acetyl-CoA was competitive with respect to CoA, and NADH was competitive with respect to NAD+ in both overall reactions, and that succinyl-CoA or acetyl-CoA and NADH were uncompetitive with respect to 2-oxoglutarate or pyruvate, respectively. However, noncompetitive (rather than uncompetitive) inhibition patterns were observed for succinyl-CoA or acetyl-CoA versus NAD+ and for NADH versus CoA. These results are consistent with the proposed mechanisms.