Microbial transformations of steroids-XII. Progesterone hydroxylation profiles are modulated by post-translational modification of an electron transfer protein in Streptomyces roseochromogenes

Abstract

When Streptomyces roseochromogenes strain 10984 was incubated with exogenous progesterone for 25 h the major monohydroxylated metabolite, 16α-hydroxyprogesterone was produced in 3.6 fold excess to the minor metabolite 2β,16α-dihydroxyprogesterone. In a reconstituted system containing highly purified progesterone 16α-hydroxylase cytochrome P-450, and electron transfer proteins ferredoxin-like redoxin (roseoredoxin) and redoxin reductase (roseoredoxin reductase), both metabolites were produced but in a 10:1 ratio. When S. roseochromogenes was pre-incubated for 8 h with 0.32 mM progesterone and the purified components of the hydroxylase system incubated as before, the ratio of 16α-hydroxyprogesterone to 2β,16α-dihydroxyprogesterone produced decreased to 2.8:1, virtually identical to the ratio in whole cell transformations. Reconstitution assays containing all combinations of hydroxylase proteins purified from progesterone pre-incubated and control cells showed that the roseoredoxin was solely responsible for the observed changes in in vitro metabolite ratios. The fact that the lower 16α-hydroxyprogesterone to 2β,16α-dihydroxyprogesterone ratio was also obtained when S. roseochromogenes was exposed to 0.335 mM cycloheximide for 8 h prior to the progesterone pre-incubation, pointed to post-translation modification of the roseoredoxin. Separation of two isoforms of roseoredoxin by isoelectric focusing supported this proposition.