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

Publisher Website
Google Scholar
Abstract
Studies were conducted on the influence of level of protein intake, starvation, or feeding a protein-free diet on the activities of L-leucine:α-ketoglutarate aminotransferase and α-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 α-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.