Abstract
The effects of dietary lysine and protein levels on liver and kidney lysine-ketoglutarate reductase (LKGR) activities and on the oxidation oflysine to expired CO2 were studied in weanling rats. Liver LKGR activity in rats fed 20% wheat gluten diets supplemented with 1.0 and 5.0% lysine •HCl reached a maximum at 7 to 10 days. At levels below 0.5% lysinea•HCl supplementation, liver LKGR maintained a low activity, but above this intake level, the activity increased linearly with increased lysine. Liver LKGR activity also increased with graded levels of dietary casein. A similar response to dietary lysine and casein levels was observed in kidney LKGR, but was a lesser degree. The oxidation of lysine to expired CO2 after intraperitoneal injection of L-lysine-U-14C was greatly elevated as dietary lysine or casein levels increased, and the response pattern was quite similar to that of the liver LKGR activity. Results with wheat gluten suggest that the estimation of liver LKGR activity as well as the lysine oxidation technique provides a method for measuring the requirement for lysine in the growing rat.
