Substrate access channel geometry of soluble and membrane-bound cytochromes P450 as studied by interactions with type II substrate analogues.

The problems of alterations in the tertiary structure at the cytochrome P450 active site after isolation from the microsomal membrane and comparative analysis of the structures of the active sites of membrane-bound P450 and soluble P450cam have been studied in terms of using bifunctional compounds (I-IV). These amphiphilic compounds contain a pyridine radical, an aliphatic chain of variable length (n), and diphosphonic acid at the end of the molecule. There exists an optimal length (n) at which the interaction between I-IV and P450 is rather efficient. Comparison of the data on such interactions with microsomal P450, as well as P450 isolated from the membrane in oligomeric and monomeric states, and P450cam allows the estimation of the distance between the Fe3+ ion in the active site and the charged residues (Lys/Arg) on the enzyme surface (approximately 17 A for all P450s).