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Influence of Dietary Nitrogen Intake on Mammalian Branched Chain -Keto Acid Dehydrogenase Activity¹

Institute of Physiological Chemistry, University of Erlangen-Nuremberg, Fahrstr. 17, 8520 Erlangen, West Germany

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 -keto acid dehydrogenase (BCKAD) activity. Km values measured with -ketoisocaproate and -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.

KEY WORDS: • -keto acid dehydrogenase • casein • amino acids • Km-values

¹ Supported by grants from the Jacques-Pfrimmer-Gedächtnisstiftung.

Manuscript received 19 March 1981.