Cytochrome P450 system

The cytochrome P450 system(1) consists of oxidizing
enzymes (mixed monooxygenases).
They represent the first phase of detoxification:
a substrate (RH) is oxidized to ROH utilizing atmospheric
oxygen (O2), with water (H2O) being
formed as a byproduct. A reductase delivers hydrogen
ions (H+) either from NADPH or NADH. A
characteristic feature of P450 enzymes (2) is
that a single chemical substrate can frequently
be degraded by several P450 enzymes and that
a single P450 protein can oxidize a number of
structurally different chemical substances. The
capacity to metabolize and detoxify a wide
range of chemical substances is considerable.
However, the enzyme activities of phase I and
phase II must be well coordinated, since toxic
intermediates with undesirable side effects occasionally
arise in the initial stages of phase II.