Cystathionine synthetase and cystathionase activities in the fat body during fifth instar larval stage of the silkworm, Bombyx mori

Abstract

The highest activities of cystathionine synthetase and cystathionase in fifth instar larvae of the silkworm, Bombyx mori, were found in the fat body. The activity of both enzymes in this tissue was higher in males than in females throughout the fifth instar, with the largest difference occurring in cystathionase activity. The relatively low level of cystathionine found in the haemolymph of males compared to females may be due to a difference in the rate of degradation of cystathionine by cystathionase rather than to a difference in its rate of synthesis by cystathionine synthetase in the fat body. Other tissues had lower levels of cystathionine synthetase and cystathionase activities which were the same for both sexes. Extirpation of the gonads did not affect the activities of the enzymes in the fat body.