P450BM-3 and other inducible bacterial P450 cytochromes: biochemistry and regulation.

When I began this review my goal was to present a coherent overview of the biochemistry and regulation of the inducible P450 cytochromes of bacteria. Now, at the end, I wonder if a unified perspective is possible at this time. On the basis of admittedly limited data, bacterial P450 systems seem as different from each other as they are, as a group, from the mammalian P450 cytochromes. The most obvious physical difference between the bacterial monooxygenases and their mammalian counterparts is solubility; with several possible exceptions (69, 70, 76), bacterial P450s are soluble whereas the microsomal and mitochondrial P450s are membrane-associated proteins. In structure and organization, however, the few well-characterized prokaryotic P450-dependent systems vary widely. The three-component arrangement is probably most common but even here variation is apparent. The P450cam putidaredoxin reductase contains only FAD and is quite specific for NADH (35, 39); the P450meg megaredoxin reductase contains only FMN and is specific for NADPH (59, 60). Putitive two-component P450 systems in bacteria have not yet been adequately characterized but the P450oct and P450npd monooxygenases (69, 70, 93) could well be organized in this way. The catalytically self-sufficient P450BM-3 is currently the only single-component P450-dependent monooxygenase known but additional examples of this arrangement may well be found in other bacteria. Paradoxically, P450BM-3 is structurally much more analogous to liver microsomal P450 systems than to any other bacterial P450 monooxygenase characterized to date. Another generally recognized difference between prokaryotic and eukaryotic P450s pertains to function; most known bacterial P450-dependent systems initiate the oxidation of recalcitrant carbon compounds so that the hosts can utilize them as sole carbon sources for growth. Some lower eukaryotes [certain yeasts, for example (134)] also employ P450-dependent systems in this way but, among most fungi as well as in higher eukaryotes, P450 cytochromes are involved in specific pathways of sterol or other lipid syntheses or, as in the mammalian liver microsomal systems, in detoxification reactions.(ABSTRACT TRUNCATED AT 400 WORDS)