Enzymic Synthesis of Juvenile Hormone in Locust Corpora Allata: Evidence for a Microsomal Cytochrome P‐450 Linked Methyl Farnesoate Epoxidase

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Abstract
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 d204 1.13–1.15, whereas NADPH-cytochrome c reductase and NADPH–dependent methyl farnesoate 10, 11-epoxidase activities band identically between d204 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 × 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.

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