Comparison of methionine metabolism in symbiotic and aposymbiotic larvae of Sitophilus oryzae L. (Coleoptera: Curculionidae)—I. Evidence for a glycine N-methyltransferase-like activity in the aposymbiotic larvae

Abstract

1. 1. Sarcosine and methionine metabolisms were investigated in symbiotic and aposymbiotic strains of the weevil Sitophilus oryzae. The follow-up of these two amino acids during larval and pupal development showed that they had opposite variations and suggested that they were involved in the same metabolic pathway. 2. 2. The index of methylation, three times higher in the aposymbiotie larvae than in the symbiotic larvae, indicated that the tissues of aposymbiotic larvae were more suitable for transmethylations than the tissues of symbiotic larvae. 3. 3. Nutritional experiments with methionine and glycine gave evidence that these two amino acids were involved in sarcosine biosynthesis in the weevils. The addition of ethionine, an inhibitor of methyltransferases, to the diet resulted in a decrease in the levels of sarcosine in both strains. 4. 4. It is therefore suggested that sarcosine biosynthesis in the aposymbiotic larvae of S. oryzae results probably from a glycine N-methyltransferase-like activity, though such an enzyme is at the present time unknown in insects.