TERMINAL STAGES IN JUVENILE-HORMONE BIOSYNTHESIS IN CORPORA ALLATA OFDIPLOPTERA-PUNCTATA - DEVELOPMENTAL-CHANGES IN ENZYME-ACTIVITY AND REGULATION BY ALLATOSTATINS

The O-methyltransferase, which is responsible for the methylation of f arnesoic acid in the corpora allata of Diploptera punctata, is a cytos olic enzyme. The activity of O-methyltransferase closely parallels JH biosynthesis in last instars and adult females. Because allatostatin 4 (AST 4) from D. punctata and callatostatin 5 (CAST 5) from Calliphora vomitoria can inhibit juvenile hormone biosynthesis, their effects on the activity of O-methyltransferase and epoxidase, the enzymes involv ed in the final two steps of juvenile hormone biosynthesis, were inves tigated in vitro. AST 4 can inhibit methyltransferase activity whereas CAST 5 stimulates it. AST 4 inhibits epoxidase activity slightly wher eas CAST 5 inhibits it significantly (36%). Treatment of corpora allat a with farnesoic acid (40 mu M can reverse the inhibitory effect of AS T 4 and CAST 5 on JH release by corpora allata. Thus, allatostatins ap pear to exert their inhibitory effect on JH biosynthesis at least part ially through inhibition of the activity of terminal enzymes. Two bios ynthetic pathways for the conversion of farnesoic acid to JH may exist in corpora allata of D. punctata: the predominant pathway is farnesoi c acid to methyl farnesoate, then to JH whereas the other, representin g about 5-1O% of total JH production, is farnesoic acid to JH III acid , then to JH.