Cytochrome P-450 from mitochondria of bovine adrenal cortex Comparison of cholesterol side-chain cleavage P-450 with steroid 11β-hydroxylation P-450 and immunochemical cross-reactivity between adrenal mitochondrial and liver microsomal cytochromes P-450

Adrenocortical mitochondrial cytochrome P?450 specific to the cholesterol side-chain cleavage (desmolase) reaction differs from that for the 11β-hydroxylation reaction of deoxycorticosterone. The former cytochrome appears to be more loosely bound to the inner membrane than the latter. Upon ageing at 0°C or by aerobic treatment with ferrous ions, the desmolase P-450 was more stable than the 11β-hydroxylase P-450. By utilizing artificial hydroxylating agents such as cumene hydroperoxide, H₂O₂, and sodium periodate, the hydroxylation reaction of deoxycorticosterone to corticosterone in the absence of NADPH was observed to a comparable extent with the reaction in the presence of adrenodoxin reductase, adrenodoxin and NADPH. However, the hydroxylation reaction of cholesterol to pregnenolone was not supported by these artificial agents.Immunochemical cross-reactivity of bovine adrenal desmolase P-450 with rabbit liver microsomal P-450_LM4 was also investigated. We found a weak but significant cross-reactivity between the adrenal mitochondrial P-450 and liver microsomal P-450_LM4, indicating to some extent a homology between adrenal and liver cytochromes P-450.