Bifunctional compound study of the active-centre location of cytochrome P-450 in a microsomal membrane ('float'...

A new approach, which we call 'float' molecules method for the determination of the active-centre location of cytochrome P-450 in a microsomal membrane, is proposed. We have synthesized new bifunctional compounds with the general formula: R-(CH2)n-S-CH2-CH(PO3H2)2, where n = 0,3,5,6,7,10 and R is a naphthalene-containing radical. The compounds inhibit oxidation and binding of cytochrome P-450 substrates of type I (naphthalene, aminopyrine) and of type II (aniline). The inhibition is of a competitive character. Compounds (I-V) neither affect NADPH-cytochrome c reductase, nor induce conversion of cytochrome P-450. A lipid-soluble fluorescent probe (1,6-diphenyl-1,3,5-hexatriene) has been used to show that these compounds do not affect melting of microsomal membrane. The 31P-NMR method has demonstrated compound (III) to be incorporated into microsomal membrane so that the hydrophilic part is in the water phase. The data obtained make it possible to estimate the distance (r) between the membranes surface and Fe3+ in the active centre of the enzyme (r less than or equal to 20 A) under the assumption that all molecules of cytochrome P-450 are equally remote from the membrane surface.