The Steroid-9α-Hydroxylation System from Nocardia Species

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Abstract
The steroid 9α-hydroxylase from Nocardia species M117 was found to be an electron-transport chain consisting of an NADH-dependent flavoprotein reductase and two iron-sulfur proteins named protein II and protein III. The components were partially purified. The flavoprotein reductase from Nocardia species M117 was enriched 20-fold to 100 units/mg and protein III 200-fold to 2400 units/mg protein. Protein II has a molecular weight of approximately 214000. The purification factor of protein II was not determined. The absorption spectrum of protein II shows a maximum at 425 nm in the oxidized form and maxima at 510 nm, 415 nm and 370 nm in the reduced state; whereas protein III has a prominent maximum at 452 nm in the oxidized form and no absorption maximum in the reduced state. Carbon monoxide treatment of the reduced forms of protein II and protein III showed no maximum at 450 nm. Both proteins II and III are sensitive to oxygen. The hydroxylase activity can be reconstituted from the isolated components. Activity of the combined proteins was demonstrated by product analysis and NADH consumption produced by the addition of progesterone. Protein III catalyzes the reduction of cytochrome c in the presence of NADH and Nocardia flavoprotein reductase. The reconstitution of hydroxylase activity from cytochrome-free enzyme preparations excludes the participation of cytochrome P-450 in this steroid hydroxylase system.