Adenosine 5'-triphosphate- yielding pathways of branched-chain amino acid fermentation by a marine spirochete.
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 CO(2) 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.
D000085:Acetates / Q000378:metabolism; D019342:Acetic Acid; D000217:Acyltransferases / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism*; D000693:Anaerobiosis; D005285:Fermentation; D007532:Isoleucine / Q000378:metabolism*; D007930:Leucine / Q000378:metabolism*; D010770:Phosphotransferases / Q000378:metabolism; D012623:Seawater; D013144:Spirochaetales / Q000378:metabolism*; D000637:Transaminases / Q000378:metabolism; D014633:Valine / Q000378:metabolism*
D000085:Acetates; D007532:Isoleucine; D000255:Adenosine Triphosphate; D000217:Acyltransferases; D000637:Transaminases; D010770:Phosphotransferases; D007930:Leucine; D014633:Valine; D019342:Acetic Acid