Evidence for cytochrome P-450 multiplicity in the midgut of the cluster caterpillar, Spodoptera litura (F.)

Abstract

Treatment of Spodoptera litura (F.) (the cluster caterpillar) larvae with geraniol (0.4%), pentamethylbenzene (0.2%), β-naphthoflavone (0.2%), and phenobarbital (0.1%) increased cytochrome P-450 content, with geraniol causing a four-fold induction (no differential induction of cytochrome P-450 monooxygenase activity was observed). All treatments, except phenobarbital, increased aldrin epoxidase, ethoxyresorufin-, and ethoxycoumarin- O-deethylase activities. Only geraniol treatment induced epoxide hydrolase activity. Ethoxyresorufin and ethoxycoumarin- O-deethylase activities were insensitive to carbon monoxide and metyrapone inhibition. In contrast, aldrin epoxidase was sensitive to both inhibitors. Differential inhibition was also seen with α-naphthoflavone with the O-deethylase activities being more inhibited than aldrin epoxidase at equal inhibitor concentration. Subsequent studies with isosafrole (0.05%) resulted in qualitative changes in midgut microsomal cytochrome P-450 parameters compared to geraniol (0.4%) and control microsomes. Isosafrole treatment greatly induced ethoxyresorufin- (∼20-fold) and ethoxycoumarin- O-deethylase activity while only slightly inducing aldrin epoxidase activity (∼2-fold). Isosafrole treatments altered the apparent K m for ethoxyresourufin and ethoxycourmarin and increased the proportion of low-spin cytochrome P-450 present in midgut microsomes. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of isosafrole-treated microsomes revealed the presence of two protein staining bands of molecular weights 53,500 and 50,500 not observed in control or geraniol-induced microsomes. The results suggest that like S. eridania multiple forms of cytochrome P-450 are present in S. litura midgut microsomes.