Plasma concentrations of amino acids and α-ketoisocaproate and α-keto-γ-methiolbutyrate decarboxylation activities in livers of rats trained to eat 9 or 50% casein diets for 5 hours/day, were measured one-half hour before and one-half and 3 hours after the start of the feeding period. Decarboxylation of both α-ketoisocaproate and α-keto-γ-methiolbutyrate by liver increased significantly within one-half hour after rats had ingested either the 9 or the 50% casein diet. Liver decarboxylation activity of rats fed the 50% casein diet was from two- to fivefold higher than that of rats fed the 9% casein diet. The greatest difference was observed when calcium, NAD and coenzyme A were included in the decarboxylation assay medium. Although the activity of the branched-chain α-keto acid dehydrogenase increased in response to food ingestion, plasma concentrations of branched-chain amino acids also increased greatly after the ingestion of food. The similarity in the responses of α-ketoisocaproate and α-keto-γ-methiolbutyrate decarboxylation in rats fed diets differing in protein content and subjected to different feeding regimens allows us to suggest that the branched-chain α-keto acid dehydrogenase is responsible, in part, for the oxidative decarboxylation of the α-keto acid analog of methionine.
All Science Journal Classification (ASJC) codes
- Medicine (miscellaneous)
- Nutrition and Dietetics