A CYTOCHROME-P450 TERPENOID HYDROXYLASE LINKED TO THE SUPPRESSION OF INSECT JUVENILE-HORMONE SYNTHESIS

A cDNA encoding a cytochrome P450 enzyme was isolated from a cDNA libr ary of the corpora allata (CA) from reproductively active Diploptera p unctata cockroaches. This P450 from the endocrine glands that produce the insect juvenile hormone (JH) is most closely related to P450 prote ins of family 4 and was named CYP4C7, The CYP4C7 gene is expressed sel ectively in the CA; its message could not be detected in the fat body, corpora cardiaca, or brain, but trace levels of expression were found in the midgut and caeca, The levels of CYP4C7 mRNA in the CA, measure d by ribonuclease protection assays, were linked to the activity cycle of the glands. In adult females, CYP4C7 expression increased immediat ely after the peak of JH synthesis, reaching a maximum on day 7, just before oviposition, mRNA levels then declined after oviposition and du ring pregnancy. The CYP4C7 protein was produced in Escherichia coli as a C-terminal His-tagged recombinant protein. In a reconstituted syste m with insect NADPH cytochrome P450 reductase, cytochrome b(5), and NA DPH, the purified CYP4C7 metabolized (2E,6E)-farnesol to a more polar product that was identified by GC-MS and by NMR as (10E)-12-hydroxyfar nesol. CYP4C7 converted JH III to 12-trans-hydroxy JH III and metaboli zed other JH-like sesquiterpenoids as well. This omega-hydroxylation o f sesquiterpenoids appears to be a metabolic pathway in the corpora al lata that may play a role in the suppression of JH biosynthesis at the end of the gonotrophic cycle.