Effects of cholesterol side-chain groups and adrenodoxin binding on the vibrational modes of carbon monoxide bound to cytochrome P-450scc: implications of the productive and nonproductive substrate bindings.

Effects of the bindings of cholesterol and its hydroxylated analogues on the Fe-CO stretching and the C-O stretching vibrations of cytochrome P-450scc-CO complex were examined by resonance Raman and FT-IR spectroscopies to reveal the spatial relationship between the steroid side-chain groups and the heme-bound C-O moiety at the active center. These C-O and Fe-CO vibrations exhibited considerable variations depending on the steroids used; however, analyses on the nu Fe-CO vs nu C-O plot for cytochrome P-450scc indicated the absence of the negative correlation between these two vibrations, which is common among various Fe(2+)-porphyrin-CO complexes having imidazole ligands. Rather, we noticed the existence of two groups depending on substrates, the one exhibiting C-O infrared absorption bands in the region from 1930 to 1940 cm-1 and higher enzymatic turnover numbers in the reconstituted enzymatic systems and the other exhibiting C-O infrared absorption bands in the region above 1945 cm-1 and lower enzymatic turnover numbers. Thus, the former substrate group is likely to be fitted into the substrate binding site in the efficient "productive substrate binding" structure, whereas the latter group may be bound to the enzyme in the structure not suitable for the efficient enzymatic reaction ("nonproductive substrate binding" conformation).(ABSTRACT TRUNCATED AT 250 WORDS)