Aldehydic products of lipid peroxidation inactivate cytochrome P-450

The effects of aldehydic products of lipid peroxidation, malondialdehyde (MDA) and 4-hydroxynonenal (HNE), on the structure of rat liver microsomal membrane and cytochrome P-450 was studied. MDA (15-30 mu M) similarly to p-chlormercuribenzoate decreased the cytochrome P-450 content by 50 % and lowered microviscosity of lipid surrounding of the spin label OTMB bound to SH-groups of membrane proteins. OTMB was effectively reduced by K3Fe(CN)(6) in microsomes preincubated with MDA (20 (M), but not in native microsomes. HNE (10 mu M) decreased the cytochrome P-450 content by 90 %. Reduced glutathione and cysteine (5 mM) prevented the decrease of cytochrome P-450 under influence of both MDA or HNE, whereas cytochrome P-420 formation remains unchanged. MDA and HNE decreased activities of NADPH oxidase and NADPH cytochrome c reductase. HNE increased microviscosity of the OTMB lipid environment. The further increase of HNE concentration did not affect this parameter. Both MDA and HNE increased the absorbance at 420 nm, which indicated inactivation of cytochrome P-450 by changes in hydrophobicity of lipid surrounding. We suggest that HNE and aliphatic aldehydes at low concentrations can enter into hydrophobic environment of cytochrome P-450 binding to its SH-groups, which led to inactivation of cytochrome P-450. At the same time, the modification of membrane surface layer and subsequent decrease of hydrophobicity of cytochrome P-450 environment preceded the binding of MDA to SH-groups of cytochrome P-450 to develop its inactivating effect.