Structural–functional organization of cytochrome P450 containing monooxygenase and some aspects of modeling

The article deals with a superfamily of monooxygenases, a multienzymeproteinaceous complex containing cytochrome P450 as a terminal electron acceptor. Due to the low substrate specificity, this monooxygenase actively participates in biosynthesis and oxidation of numerous endogenous cell compounds, and also in oxidation and detoxification of wide spectrum of compounds that are foreign to an organism (xenobiotics). The main peculiarity of animal monooxygenase is its interaction with the membrane: all three components of it are true membrane proteins that gain some advantages (binding of hydrophobic substrates to cytochrome P450, creation of optimal conditions by reaction with its own reductase, modulation of electron transport, etc) over other soluble oxidases. In plants, cytochrome P450 is embedded in the membrane but simultaneously, it occurs in a soluble form as well. As a result, a stronger protection barrier against the impact of xenobiotic-toxicants is created in it. In addition, it is shown that in plants, the same isoforms of cytochrome P450 participate in biosyntheses and xenobiotic degradation. Penetration of xenobiotics into a plant cell and especially, its polarity represents a regulatory signal, which ensures proper distribution of hemoprotein pool in these processes. Action mechanism of cytochrome P450, i.e. the functioning of monooxygenase cycle and its completion stage, when oxygen activated by two electrons is inserted into the substrate and hydroxylation product is formed, is described in more detail. Nowadays, functional models of monooxygenases are used effectively to study this stage. It is considered that in oxygenase reaction, oxygen atom formed by its interaction with ferric ion complex and redox-active ligand is transferred to the substrate via so-called oxenoid mechanism. The rate of the whole hydroxylation process is limited by the stage of insertion of activated oxygen into the substrate. It deserves consideration that hydroperoxides, which are reduced by two electrons and perform shunting of the cycle, model incompletely its operation. Action mechanism of monooxygenase essentially differs from this model and the cycle prefers phasic successive proceeding.