Evidence for an Impairment in the Conversion of Methionine to Cysteine in the Selenium-Deficient Chick

Abstract

Abstract

Experiments were conducted to determine the effects of dietary sulfur-containing amino acids on the etiology of nutritional pancreatic atrophy (NPA) in the Se-deficient chick. Supplementation of a crystalline amino acid diet containing 0.82% methionine with 0.4% L-cystine resulted in significant improvements in growth, efficiency of feed utilization and chick survival, whereas supplementation with 0.4% L-methionine had no effect. L-Cystine supplementation did not significantly affect plasma Se-dependent glutathione peroxidase activity, or prevent NPA. The addition of graded levels of L-cystine to a diet marginally adequate in methionine resulted in maximal gain in body weight and efficiency of feed utilization with 45 mmole half-cystine equivalents per kilogram. Supplementation of the same diet with equimolar amounts of L-methionine did not show significant improvements in these parameters unless the diet was also supplemented with Se. Plasma-free amino acid analyses showed significant reductions in the concentrations of cysteine, cystathionine, and homocysteine in Se-deficient chicks. These data indicate than an impairment in the metabolic synthesis of cysteine in the Se-deficient chick is responsible for a major portion of the growth depression observed with severe uncomplicated Se deficiency. This effect of selenium, however, is distinct from that in preventing NPA.