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Degradation of Lysine in Chicks¹

Department of Poultry Science and Graduate School of Nutrition, Cornell University, Ithaca, New York 14850

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 reductase are 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 ¹⁴CO₂ production which was stimulated by O₂ and -ketoglutarate. Under these conditions, pipecolic acid accumulated as the major metabolite and was readily oxidized to ¹⁴CO₂ by chick liver homogenates. When L-lysine-U-¹⁴C was incubated anaerobically with liver homogenates or mitochondria along with -ketoglutarate and NADPH, ¹⁴C-saccharopine accumulated as the major metabolite. Both L-amino acid oxidase and lysine-ketoglutarate reductase were affected by dietary tratments in these studies. The activity of liver lysine-ketoglutarate reductase was consistently lower in the HA strain than in the LA strain fed various types of diets, but no difference in the activities of liver L-amino acid oxidase could be detected in the HA and LA chicks. These data provide additional evidence that the saccharopine pathway may be the major pathway for L-lysine degradation in vivo in chicks. The strain differences in liver lysine-ketoglutarate reductase activity observed may account for variation in lysine metabolism and in part for the different dietary requirements of arginine of the two strains.

KEY WORDS: • lysine degradation • pipecolic acid • saccharopine • lysine-ketoglutarate reductase

¹ Supported in part by Public Health Service Grant no. AM06850 from the National Institute of Arthritis and Metabolic Diseases.

Manuscript received 9 December 1971.