[Selective chemical modification of cholesterol hydroxylating cytochrome P-450 from adrenal cortex mitochondria by...

Selective chemical modification of adrenocortical cytochrome P-450 responsible for the key stages in steroid biogenesis has been carried out. Nitration is followed by the heme-protein inactivation and loss of enzymatic activity. Analysis of the cytochrome P-450 nitration kinetics revealed several types of tyrosine residues differing in their accessifility for the reagent. Modification of only one or two tyrosine residues brought about the enzyme inactivation. Modification was accompanied by changes in the cytochrome P-450 spectral properties. Cholesterol and adrenodoxin protected cytochrome P-450 against inactivation by tetranitromethane. The data obtained are discussed in terms of functional role of tyrosine residues in the cytochrome P-450 molecule.