Discrimination between conformational states of mitochondrial cytochrome P-450scc by selective modification with...

Electrophoretically homogeneous cytochrome P-450scc preparation isolated by the standard method from adrenal cortex mitochondria comprises two protein forms differing in the accessibility of their amino groups to specific chemical modification with pyridoxal 5-phosphate. The protein form whose lysine amino groups are accessible to the modifier constitutes about 60-70% of the preparation. Being covalently bound to pyridoxal 5-phosphate, this protein form loses enzymatic activity and affinity for adrenodoxin. This protein form can be separated by affinity chromatography on adrenodoxin-Sepharose. The cytochrome P-450scc form whose amino groups are not accessible to the modifier is retained on the affinity matrix, and after elution from adrenodoxin-Sepharose has the absorption spectrum typical of the high-spin protein with a spectral homogeneity index A392/A278 = 1.0. The enzymatic activity of the hemoprotein form whose lysine amino groups are inaccessible to the modification is identical to that of the initial unmodified protein.