Degradation of Lysine in Chicks

Abstract

Lysine degradation in two strains of chicks selected for a high (HA) or low (LA) requirement of dietary arginine was investigated. These studies suggest that both an L-amino acid oxidase and lysine-ketoglutarate reduc A­aseare active in chick liver for the initial degradation of L-lysine, leading to the formation of pipecolic acid and saccharopine, respectively. Aerobic incubation of L-lysine-U-14C with liver homogenates or mitochondria led to 14COzproduc tion which was stimulated by Oi and a-ketoglutarate. Under these conditions, pipecolic acid accumulated as the major metabolite and was readily oxidized to 14COzby chick liver homogenates. When L-lysine-U-14C was incubated anaerobi- cally with liver homogenates or mitochondria along with o-ketoglutarate and NADPH, C-saccharopine accumulated as the major metabolite. Both L-amino acid oxidase and lysine-ketoglutarate reducA­ase were affected by dietary treat ments in these studies. The activity of liver lysine-ketoglutarate reducA­ase was consistently lower in the HA strain than in the LA strain fed various lypes of diels, bui no difference in Ihe activities of liver L-amino acid oxidase could be detected in the HA and LA chicks. These data provide additional evidence thai Ihe saccharopine palhway may be Ihe major palhway for L-lysine degradation in vivo in chicks. The slrain differences in liver lysine-keloglutarate reducA­ase activity observed may account for variation in lysine metabolism and in part for the different dietary requirements of arginine of the two strains. J. Nutr. 102: 583-596, 1972.