“…-propanone), inhibits a number of hydroxylation reactions catalyzed by cytochrome P-450. Metyrapone has a moderately broad spectrum of action for it inhibits steroid hydroxylations at C-ll/3, C-18, and C-19 in adrenal cortex (Dominguez and Samuels, 1963;Sanzari and Perón, 1966;Gaunt et al, 1968;Kahnt and Neher, 1971) and drug hydroxylations in liver microsomes (Leibman, 1969;Netter et al, 1969;Hildebrandt, 1972;Roots and Hildebrandt, 1973a,b) and in bacteria (Peterson et al, 1971;Gunsalus et al, 1971), but it has no effect on the 20aand 22-hydroxylations which are required for cholesterol side-chain cleavage in adrenal cortex mitochondria (Wilson and Harding, 1973) and on the steroid 21-hydroxylation in adrenal cortex microsomes (Dominguez and Samuels, 1963;Sweat et al, 1969a). The inhibitor effect of metyrapone is accompanied by a typical modification of the difference spectrum of P-450, characterized by the appearance of a peak at 427 nm and of a trough at 410 nm and also by a shift in the low-field electron paramagnetic signal of oxidized P-450 (Wilson et al, 1969).…”