[Cytochrome P450--its significance in the biotransformation of xenobiotics and interspecies comparisons].

Enzyme system of cytochrome is the most important system of the oxidative biotransformation of xenobiotics. It was formerly assumed to be mainly a system of detoxication, however, it was recognized to be involved in many reactions leading to biological activation of compounds. This activation may give rise to unwanted products with rather detrimental effects. Isoforms of cytochrome are classified according to the similarity in primary structures into families and subfamilies. The great variability observed in enzymatic activities and in levels of particular isoforms is based on the known genetic polymorphism and on the enzyme induction or inhibition. However, this may be reflected in different pharmacologic responses to many drugs. Due to existence of interspecies differences in the presence of cytochrome P450 isoforms as well as due to differences in the substrate specificity it is difficult to extrapolate results obtained in experiments on animals to the human cases. A survey of isoforms, important for biotransformation of xenobiotics and of their properties is presented.