Effect of blood plasma lipoproteins on hydroxylation of benzo[a]pyrene in liver microsomes of rats

Abstract

This work presents the characteristics of the catalytic activity of hydroxylation of benzo[a] pyrene (B[a]P) in rat liver microsomes using plasma lipoproteins (LP) (VLDL, LDL, HDL) as transport forms of B[a]P. The aim of the study was: to study the effect of the LP-component of the LP-B[a]P complexes on the rate of B[a]P hydroxylation in rat liver microsomes. The studies were carried out on the microsomal fraction of rat liver using B[a]P as a substrate, ultracentrifugation of individual fractions of VLDL, LDL, HDL plasma, and spectrofluorimetric determination of the activity of arylhydrocarbonhydroxylase. In work on microsomes of rat liver the rate of hydroxylation of B[a]P in free form and in the form of B[a]P complexes with various fractions of LP was analyzed. The analysis showed that the arylhydrocarbonhydroxylase activity (pmol 3-OH-B[a]P in 1 min per 1 mg of protein) decreases in the complex form B[a]P with LP. So for transport form B[a]P with HDL the decrease was by 22%, for transport form B[a]P with VLDL the decrease was 30%, and for transport form B[a]P with LDL it was 52%. It should be noted that Km for the substrate remained practically unchanged in all forms. The Vmax and Km values indicate that the LP component in complexes with B[a]P can be a noncompetitive inhibitor of B[a]P hydroxylation in rat liver microsomes.

Keywords

• benzo[a]pyrene
• rat liver microsomes
• blood plasma lipoproteins