Effect of Dietary Excesses of Lysine and Arginine on the Degradation of Lysine by Chicks

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Abstract
The factors influencing lysine degradation were investigated by studying the level of liver lysine-ketoglutarate reductase (the initial degradative enzyme) and the conversion of 14C-lysine to 14CO2 in the intact chick. Liver lysine-ketoglutarate reductase activity was increased by excesses of dietary lysine, but not arginine, and kidney arginase activity was increased by excesses of both arginine and lysine. The rate of 14CO2 production from 14C-lysine in vivo was correlated with the lysine-ketoglutarate reductase activity measured in vitro when a loading dose of lysine was given. No correlation was observed when a trace dose was given. The rate of lysine oxidation was stimulated by lysine, but excesses of dietary arginine did not increase lysine oxidation. Genetic differences in lysine-ketoglutarate reductase and the rate of 14C-lysine oxidation were observed between the high arginine and low arginine requirement strains. These findings suggest that the rate of lysine oxidation in vivo may be regulated by the lysine pool at low levels of dietary lysine, and by the level of degradative enzyme at high levels of dietary lysine.