Fluidity of the microsomal membrane and cytochrome P450 reduction kinetics of pig liver microsomes as a consequence of organic solvent impact.
ABSTRACT 1. The effect of the aromatic solvents toluene, xylene and ethylbenzene on microsomal membrane fluidity and anaerobic NADPH-reduction kinetics were studied. 2. The relation of membrane fluidity to the kinetics of cytochrome P450 reduction by NADPH-cytochrome P450 reductase was examined with regard to a membrane-mediated molecular organization of the multienzyme components of the monooxygenase system. 3. Membrane fluidity changes were detected with the steady-state pyrene excimer formation method and with fluorescence lifetime measurements after incubation of the microsomes with organic solvents. 4. Increase in membrane fluidity in presence of organic solvents leads to a small but significant decrease of the rate constant of the cytochrome P450 reduction kinetics and a change in the relative amplitudes of the components of the biphasic response. 5. The results support the idea of a molecular organization of cytochrome P450 in clusters. Fluidization of the microsomal membrane by organic solvents increase the cytochrome P450 cluster formation.
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ABSTRACT: Aliphatic, alicyclic and aromatic hydrocarbons interact with biological membranes. Until now little has been known about their mode of interaction with the membrane bilayer and membrane integral proteins with toxic effects to cells. The lipid theory hypothesis explains the toxic effects by the organic solvent-induced disorder in the lipid bilayer, which indirectly affects the function of membrane-embedded proteins. The extent of bilayer perturbations is ascribed to the solvent accumulation in the bilayer, which is related only to the lipophilicity of the molecule, independent of the chemical structure. In this study the fluidizing effects of aliphatic, alicyclic and aromatic hydrocarbons were compared. Membrane fluidity changes were estimated from the pyrene excimer formation, using pyrene and pyrene derivatives to label specifically the localization of solvent molecules in the transverse plane of the bilayer. Liposomal, microsomal and synaptosomal membrane preparations were evaluated because proteins and cholesterol, as natural membrane components, increase the bilayer order and reduce the organic solvent membrane/buffer partition. In the concentration range investigated, only the aromatic solvents disorder the lipid bilayer, with the greatest perturbation in the centre of the bilayer. These results are related to structural properties of the organic solvents investigated.Toxicology in Vitro 04/1996; 10(2):111-5. DOI:10.1016/0887-2333(95)00103-4 · 3.21 Impact Factor
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ABSTRACT: The effects of a 100 mg.kg -1 dose of benzene, an occupational and environmental toxicant, were investigated on serum, estradiol and testosterone concentrations as well as lactate dehydrogenase (LDH), alkaline phosphatase (ALP), alanine amino transferase (ALT), aspartate amino transferase (AST), and pyruvate kinase (PK) activities in the liver and kidney of rats after 2, 4, 8, 16, 32, 64 and 72 hours. Benzene was given intraperitoneally to Rat rattus norvegicus and the control groups were injected with physiological saline. Liver tissue LDH, AST, ALT and kidney tissue LDH, ALP, AST, ALT activities were lower in the benzene treated group when compared to those in the control group (p<0.05). A tendency for an increase in the liver tissue ALP activity was observed, which was significant at 8 and 16 hours (p<0.05). There were significant increases in ALT in the liver and LDH, AST, and ALT enzyme activities in the kidney tissue at the beginning of the experiment in both groups and these activities were found to be nearly the same. Pyruvate kinase enzyme activities in rats given benzene were slightly increased in kidney tissues but lower in liver tissues. Differences between the groups tended to disappear towards the end of the experimental period. However, serum estradiol concentrations in the serum diverged significantly (p<0.05). Consequently, it was found that benzene administration led to some changes (increases then decreases) in LDH, ALP, ALT, AST, and PK activity and estradiol, testosterone concentrations in different tissues of rats. Possible causes of the increases and decreases in enzyme activities and hormone levels are discussed.Acta veterinaria 01/2003; DOI:10.2298/AVB0303087D · 0.13 Impact Factor