Influence of dietary nitrogen intake on mammalian branched chain alpha-keto acid dehydrogenase activity.

Male albino rats (100-130 g) were fed diets of varying casein contents for a period of six days. Increasing the casein content from 0.38% to 22% led to an elevation of hepatic branched chain alpha-keto acid dehydrogenase (BCKAD) activity. Km values measured with alpha-ketoisocaproate and alpha-ketoisovalerate as substrates were not influenced by the dietary treatment. Replacing the casein content (22%) of the diet by an equivalent amount of amino acids resulted in a significant decrease in hepatic BCKAD activity. The decrease in Vmax values was not accompanied by changes in Km-values. No enhancement of hepatic enzyme activity was observed when increasing the amino acid content of the diet from 17.5% to 25%. Changes in enzyme activity due to alterations of the dietary nitrogen source were not observed in kidney and brain.