Ronald R. Johnson

Studies on the metabolism of valine, proline, leucine and isoleucine by rumen microorganisms in vitro.

Evidence is presented that valine is oxidatively deaminated and decarboxylated by rumen microorganisms in vitro giving rise to isobutyric acid, and that proline undergoes reductive ring cleavage and deamination at the δ-position to form valeric acid. These fatty acids have been shown previously to enhance the digestion of cellulose by rumen microorganisms; thus the cellulolytic factor activity of valine and proline arises through their conversion to these fatty acids. The significant observations made on the metabolic breakdown of these amino acids were: (a) Up to 43% of the C14 in dl-valine-1-C14 can be recovered as C14O2; (6) α-ketoisovaleric acid-1-C14 was isolated from dl-valine-1-C14 reaction mixtures; (c) δ-aminovaleric acid-C14 was isolated from fermentations to which l-proline-C14 had been added; (d) as the fermentations with l-proline-C14 proceeded, an increase in the radioactivity of valeric acid was demonstrated; and (e) the proposed intermediates in valine, proline, leucine, and isoleucine metabolism were found to be cellulolytically active for rumen microorganisms in vitro.