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Dietary Influences on the Activities of Enzymes Involved in Branched-chain Amino Acid Catabolism in the Chick¹

Department of Animal Sciences, Purdue University, Lafayette, Indiana 47907

Studies were conducted on the influence of level of protein intake, starvation, or feeding a protein-free diet on the activities of L-leucine:-ketoglutarate aminotransferase and -ketoisocaproate dehydrogenase in chicks. The highest aminotransferase activity was observed in kidney followed by skeletal muscle and then liver. Increased activity of this enzyme as a result of feeding a 75% isolated soybean protein (ISP) diet occurred only in the kidney. Starvation or feeding a protein-free diet for 48 hours did not exert a marked influence on the aminotransferase activities. Similar specific but lower total activities of -ketoisocaproate dehydrogenase were noted in the kidney as compared with liver of chicks fed a 25% ISP diet with skeletal muscle being much lower. Chicks fed the 75% ISP diets had five- to 15-fold higher dehydrogenase activities in liver whereas in kidney the increase was less than twofold. No change was seen in skeletal muscle. Feeding a protein-free diet for 48 hours resulted in marked decreases in the liver dehydrogenase activities while starvation resulted in less of a decrease in chicks previously fed the 75% ISP diet and an increase in chicks previously fed the 25% ISP diet. Assays for these two enzymes using isoleucine and/or valine as substrate indicated similar activities regardless of the substrate.

KEY WORDS: • L-leucine:-ketoglutarate aminotransferase • -ketoisocaproate dehydrogenase • liver • kidney

¹ Journal paper no 4940. Purdue University Agricultural Experiment Station. This investigation supported in part by Public Health Service Research Grant AM 11487 from the National Institute of Arthritis and Metabolic Diseases.

² Present address: Department of Physiology and Pharmacology, College of Veterinary Medicine, University of Georgia, Athens, Ga. 30601.

Manuscript received 6 November 1972.