11β-Hydroxylase Activity in Recombinant Yeast Mitochondria

In mammals, the final 11β-hydroxylation step of the hydrocortisone biosynthesis pathway is performed by a mitochondrial enzyme, namely cytochrome P-45011β, together with the electron carriers adrenodoxin and NADPH adrenodoxin oxidoreductase. Successful production of a functional steroid 11β-hydroxylase activity was obtained in recombinant yeast in vivo. This conversion was achieved by coexpression of a mitochondrially targeted adrenodoxin and a modified bovine P-45011β whose natural presequence was replaced by a yeast presequence, together with an unexpected yeast endogenous NADPH-adrenodoxin-reductase-like activity. Adrenodoxin and P-45011β behave as a mitochondrial matrix and membrane protein, respectively. Saccharomyces cerevisiae apparently produces a mitochondrial protein which is capable of transferring electrons to bovine adrenodoxin, which in turn transfers the electrons to P-45011β. The endogenous adrenodoxin oxidoreductase gains electrons specifically from NADPH. The notion that a yeast microsomal NADPH P-450 oxidoreductase can transfer electrons to mammalian microsomal P-450s can be extended to mitochondria, where an NADPH adrenodoxin oxidoreductase protein transfers electrons to adrenodoxin and renders a mitochondrial mammalian P-450 functional in vivo. The physiological function of this yeast NADPH adrenodoxin oxidoreductase activity is not known.