US EPA

2179002 

Journal Article 

EFFECT OF LYSOLECITHIN ON MONOOXYGENASE ACTIVITIES IN RAT-LIVER MICROSOMES INDUCED BY METHYLCHOLANTHRENE XENOBIOTICS 

Novikov, KN; Sumbalova, Z; Timofeev, KN 

1992 

1 

Biochemistry (Moscow)
ISSN: 0006-2979
EISSN: 1608-3040 

57 

12 

1259-1267 

WOS:A1992LN46200003 

Effects of exogenous gamma-myristoyl- and gamma-palmitoyllysolecithins on physicochemical characteristics of the membranes of rat liver microsomes (eg., hydrophobicity and viscosity) and on oxidative NADPH-dependent O-deethylation of 7-ethoxycoumarin (7-EC), O-demethylation of p-nitroanisole (p-NA), and hydroxylation of 3,4-benz(a)pyrene (BP) by the monooxygenase system induced by the methylcholanthrene xenobiotics methylcholanthrene (MCh), beta-naphthoflavone (NF), and Sovol (SV) have been investigated. The specific inducible form cytochrome P-450c showed different affinity for the substrates. Lysolecithin decreased the hydrophobicity but only slightly increased membrane viscosity, whereas the monooxygenase substrates neutralized this effect. Lysolecithin (2-20 mug/mg microsomal protein) inhibited the 7-EC deethylase activity (maximally by 11%) in NF- and SV-induced microsomes, the inhibiting effect being more pronounced than that in MCh-induced microsomes. At higher concentrations lysolecithin more strongly inhibited the rate of 7-EC deethylation in MCh-induced microsomes; the maximal inhibition (23%) was observed at 60 mug lysolecithin per mg microsomal protein. With NF- and SV-induced microsomes the inhibition was 18%. The inhibiting effect of lysolecithin on 7-EC deethylation was less expressed than that on p-NA O-demethylation in induced (but not intact) microsomes. A significant positive correlation between the changes in hydrophobicity and the inhibition of the reaction rate in the presence of lysolecithin was found only for 7-EC deethylation. 

MICROSOMES; CYTOCHROME-P-450; LYSOLECITHIN; MONOOXYGENASE ACTIVITIES; METHYLCHOLANTHRENE XENOBIOTICS