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J Bacteriol. 1981 October; 148(1): 117-123
Copyright © 1981, American Society for Microbiology. All Rights Reserved.

Adenosine 5'-Triphosphate-Yielding Pathways of Branched-Chain Amino Acid Fermentation by a Marine Spirochete

¹ Department of Microbiology, University of Massachusetts, Amherst, Massachusetts 01003

ABSTRACT

The metabolic pathways utilized by an obligately anaerobic marine spirochete (strain MA-2) to ferment branched-chain amino acids were studied. The spirochete catabolized L-leucine to isovaleric acid, L-isoleucine to 2-methylbutyric acid, and L-valine to isobutyric acid, with accompanying CO₂ production in each fermentation. Cell extracts of spirochete MA-2 converted L-leucine, L-isoleucine, and L-valine to 2-ketoisocaproic, 2-keto-3-methylvaleric, and 2-ketoisovaleric acids, respectively, through mediation of 2-ketoglutarate-dependent aminotransferase activities. The branched-chain keto acids were decarboxylated and oxidized to form isovaleryl coenzyme A, 2-methylbutyryl coenzyme A, and isobutyryl coenzyme A, respectively, in the presence of sulfhydryl coenzyme A and benzyl viologen. The acyl coenzyme A's were converted to acyl phosphates by phosphate branched-chain acyltransferase enzymatic activities. Branched-chain fatty acid kinase activities catalyzed formation of isovaleric, 2-methylbutyric, and isobutyric acids from isovaleryl phosphate, 2-methylbutyryl phosphate, and isobutyryl phosphate, respectively. Adenosine 5'-triphosphate was formed during conversion of branched-chain acyl phosphates to branched-chain fatty acids. The results indicate that conversion of L-leucine, L-isoleucine, and L-valine to branched-chain fatty acids by spirochete MA-2 results in adenosine 5'-triphosphate generation. The metabolic pathways utilized for this conversion involve amino acid amino-transferase, 2-keto acid oxidoreductase, phosphate acyltransferase, and fatty acid kinase activities.

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