P450-containing systems

Any enzyme system that includes protein or domain can be called a P450-containing system.

P450 enzymes usually function as a terminal oxidase in multicomponent electron-transfer chains, called P450-containing monooxygenase systems, although self-sufficient, non-monooxygenase P450s have been also described. All known P450-containing monooxygenase systems share common structural and functional domain architecture. Apart from the cytochrome itself, these systems contain one or more fundamental redox domains: FAD-containing flavoprotein or domain, FMN domain, ferredoxin and . These ubiquitous redox domains, in various combinations, are widely distributed in biological systems. FMN domain, ferredoxin or cytochrome b₅ transfer electrons between the flavin reductase (protein or domain) and P450. While P450-containing systems are found throughout all kingdoms of life, some organisms lack one or more of these redox domains.

and some bacterial P450 systems employ soluble Fe₂S₂ ferredoxins (Fd) that act as single electron carriers between FAD-containing ferredoxin reductase (FR) and P450. In mitochondrial monooxygenase systems, adrenodoxin functions as a soluble electron carrier between NADPH:adrenodoxin reductase and several membrane-bound P450s (CYP11A, CYP11B, CYP27). In bacteria, putidaredoxin, terpredoxin, and rhodocoxin serve as electron carriers between corresponding NADH-dependent ferredoxin reductases and soluble P450s (CYP101, CYP108, CYP116).

The general scheme of electron flow in the P450 systems containing adrenodoxin-type ferredoxins is:

Eukaryotic microsomal P450 enzymes and some bacterial P450s receive electrons from a FAD- and FMN-containing enzyme known as (CPR; EC 1.6.2.4). Microsomal CPR is membrane-bound protein that interacts with different P450s. In Bacillus megaterium and Bacillus subtilis, CPR is a C-terminal domain of CYP102, a single polypeptide self-sufficient soluble P450 system (P450 is an N-terminal domain). The general scheme of electron flow in the CPR/P450 system is:

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