Intracellular signal transduction of PBAN action in the silkworm, Bombyx mori: Involvement of acyl CoA reductase

Abstract

In the silkworm, Bombyx mori, production of the sex pheromone bombykol is regulated by a neurohormone termed PBAN. We have detected the activity of acyl CoA reductase in the pheromone gland of B. mori by using palmitoyl CoA as a substrate. The acyl CoA reductase requires NADPH, but not NADH, as a proton donor. When the pheromone gland was incubated with the PBAN fragment peptide TKYFSPRLamide, palmitoyl CoA was incorporated and converted into the corresponding C 16 alcohols. Radio HPLC analysis revealed that these C 16 alcohols were hexadecan-1-ol (81.2%), (Z)-11-hexadecen-l-ol (12.3%), and (E, Z)-10, 12-hexadecadien-1-ol (= bombykol, 6.5%). The production of C 16 alcohols in the pheromone gland was inhibited by the known bombykol biosynthesis inhibitors EDTA, LaCl 3, W-7, trifluoperazine, p-nitrophenyl phosphate, NaF and compactin. By contrast, when the pheromone gland homogenate was incubated in the presence of palmitoyl CoA and NADPH, production of C 16 alcohols was affected by compactin, W-7 and trifluoperazine, but not by EDTA, LaCl 3 p-nitrophenyl phosphate and NaF. These results indicate that compactin, W-7 and trifluoperazine directly suppress the step catalyzed by acyl CoA reductase, whereas EDTA, LaCl 3 pNPP, and NaF inhibit bombykol production by affecting other biochemical steps in the signal transduction of PBAN action. The present results also imply that PBAN regulates the step catalyzed by acyl CoA reductase and that palmitoyl CoA could be used as a substrate of the acyl CoA reductase that regulates bombykol biosynthesis.