Assay of HMG-CoA synthase in Diploptera punctata corpora allata

The conversion of acetyl-CoA to HMG-CoA was measured by a radioenzymatic assay in which the product is derivatized to its bis(p-nitrobenzyl)ester and separated from the substrate by TLC. The enzymatic assay was applied to post-mitochondrial supernatants of corpora allata homogenates from the cockroach, Diploptera punctata. The apparent K_M for the conversion of acetyl-CoA to HMG-CoA was 200 μM. The enzyme activity was measured during a cycle of JH synthesis in adult mated females. HMG-CoA synthase followed the pattern of juvenile hormone III synthesis closely with a peak on day 5 (1.89 ± 0.07 nmol/h/pair-eq.), and the decline of its activity occurred earlier than that of HMG-CoA reductase.