Enzymic synthesis of juvenile hormone in locust corpora allata: evidence for a microsomal cytochrome P-450 linked methyl farnesoate epoxidase.
Homogenates of corpora allata from adult Locusta migratoria in phosphate-buffered EDTA have been analysed by sucrose-density-gradient centrifugation. Succinate-cytochrome c reductase activity (mitochondrial) bands between d20/4 1.13-1.15, whereas NADPH-cytochrome c reductase and NADPH-dependent methyl farnesoate 10.11-epoxidase activities band identically between d20/4 1.06-1.12. We conclude that the methyl farnesoate epoxidase is exclusively microsomal. Farnesoic acid O-methyltransferase is an exclusively soluble enzyme which stoichiometrically transfers the S-methyl group from S-adenosylmethionine to farnesoic acid. No carboxyl esterase activity was found. Isolated microsomes were used to obtain an apparent Km = 7.7 X 10-6 M for the epoxidase, although substrate solubility limits the rate to 0.5 V. As expected, the product (juvenile hormone III) is chiral (10 R). The epoxidase is inhibited by excess NADP+ and oxidised cytochrome c, but neither inhibited nor synergised by NADH. NADH supports less than 10% of the NADPH rate of epoxidation. The epoxidase is inhibited by a carbon monoxide/oxygen atmosphere, half-maximal inhibition occurring at a CO/O2 ratio of 4.0. This inhibition is reversed by white-light irradiation.
D000818:Animals; D002248:Carbon Monoxide / Q000494:pharmacology; D002499:Centrifugation, Density Gradient; D003335:Corpora Allata / Q000201:enzymology*; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D005231:Fatty Acids, Unsaturated / Q000378:metabolism; D005260:Female; D006110:Grasshoppers / Q000201:enzymology*; D007605:Juvenile Hormones / Q000096:biosynthesis*; D008780:Methyltransferases / Q000378:metabolism; D008861:Microsomes / Q000201:enzymology*; D009243:NAD / Q000378:metabolism; D009249:NADP / Q000378:metabolism; D010105:Oxygenases / Q000378:metabolism* / Q000528:radiation effects
D005231:Fatty Acids, Unsaturated; D007605:Juvenile Hormones; D009243:NAD; C032429:methyl farnesoate; D009249:NADP; D002248:Carbon Monoxide; D003577:Cytochrome P-450 Enzyme System; D010105:Oxygenases; C032432:methyl farnesoate epoxidase; D008780:Methyltransferases; C032433:farnesoic acid O-methyltransferase