CHARACTERIZATION AND REGULATION OF HMG-COA SYNTHASE IN LOCUSTA-MIGRATORIA CORPORA ALLATA

The conversion of acetyl-coenzyme A (CoA) to 3-hydroxy-3-methylglutaryl (HMG)-CoA was measured by a radioenzymatic assay in locust corpora allata (CA) which produce juvenile hormone (JH-III). The conversion of acetyl-CoA to HMG-COA was limited to the cytosolic fraction of the CA with an apparent K(M) = 400-mu-M. The HMG-CoA synthase activity measured during the first 15 days of the female adult life did not follow the pattern of JH-III biosynthesis. No relationship was found between JH-III release and HMG-CoA synthase activity when measured sequentially on the same CA pair. HMG-CoA synthase activity did not reflect the asymmetry in spontaneous rates of JH biosynthesis observed in left and right corpora allata. Decline of JH release after in situ transection of the nervus corporis allati 1 (NCA-1) was not associated with a decline in HMG-CoA synthase activity. The results suggest that HMG-CoA synthase activity does not have a prime influence on the spontaneous rate of JH biosynthesis, and that HMG-CoA synthase does not appear to be a target for the allatostimulating factors acting on the CA through the NCA-I.