Effects on plasma amino acid concentrations and hepatic branched-chain α-keto acid dehydrogenase activity of feeding rats diets containing 9 or 50% casein

Joseph Dixon, A. E. Harper

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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.

Original languageEnglish (US)
Pages (from-to)1025-1034
Number of pages10
JournalJournal of Nutrition
Issue number6
Publication statusPublished - Jan 1 1984
Externally publishedYes


All Science Journal Classification (ASJC) codes

  • Medicine (miscellaneous)
  • Nutrition and Dietetics

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