Nutrition and metabolism of sulphur amino acids in Argyrotaenia velutinana larvae

Abstract

Larval growth and survival to the adult stage of Argyrotaenia velutinana reared under axenic conditions and on a chemically defined diet was optimal at 0·1% dietary l-methionine level. Concentrations of 0·8% resulted in amino acid imbalance. About 75 per cent of the optimal dietary methionine requirement could be spared by l-cysteine, indicating the possibility of the conversion of methionine to cysteine via the cystathionine pathway. d-Cysteine was not as effective in sparing methionine as the l-isomer. Nutritional evidence for the presence of the cystathionine pathway was obtained as homocysteine and cystathionine spared about 75 per cent of the optimal dietary level of methionine. Inorganic sulphate did not spare the methionine requirement. Failure of larvae to grow on homocysteine in the absence of methionine suggested that homocysteine is not converted to methionine. Methionine did not spare the dietary choline requirement supporting the generalization that transmethylation reactions involving methionine and choline are impaired or absent in insects.