Induction of steroidal hydroxylase activity by plant defence compounds in the filamentous fungus Cochliobolus lunatus

We investigated the hypothesis that the endogenous role of the commercially important inducible steroid hydroxylase cytochrome P450s of fungi was in d efense against plant toxophores/secondary metabolites. Two plant defense co mpounds, the aglycones tomatidine and solanidine, the steroidal glycoalkalo id alpha-tomatine and the triterpene saponin beta-escin were tested as indu cers of 11 beta/14 alpha-steroid hydroxylase in the filamentous fungus Coch liobolus lunatus. The extracts of saponins from the roots of Primula veris and green oat leaves were also tested as inducers of 11 beta/14 alpha-hydro xylation activity in progesterone biotransformation with the same fungus. I nduction of steroid hydroxylase and inhibition of activity in some cases su pport our hypothesis that their endogenous function is in biochemical defen ce against secondary metabolites. 4-Pregnene-3,11,20-trione was added as a substrate for biotransformation with C. lunatus. We isolated from culture b roth 14 alpha-hydroxy-4-pregnene-3,11,20-trione, and the hitherto unreporte d compounds, 7 alpha,14 alpha-dihydroxy-4-pregnene-3,11,20-trone and 7 alph a-hydroxy-pregna-4,8(14)-diene-3,11,20-trione. (C) 1998 Elsevier Science Lt d. All rights reserved.