RELATIONSHIP OF FLAVONOID OXIDATION POTENTIAL AND EFFECT ON RAT HEPATIC-MICROSOMAL METABOLISM OF BENZENE AND PHENOL

The effect of several flavonoids on the benzene hydroxylase and phenol hydroxylase activity of rat hepatic microsomes was determined. The el ectrochemical characteristics of the flavonoids were also determined. The effect of flavonoids on microsomal phenol hydroxylase activity was found to correlate well with the oxidation potential for flavonoid ag lycones. Easily oxidized flavonoids inhibited phenol hydroxylase activ ity with the extent of inhibition correlated to the ease of oxidation. This inhibition exhibited dose-dependent behaviour, with concentratio ns below 1 muM having no effect. On the other hand, flavonoids with hi gh oxidation potentials increased phenol hydroxylase activity in a dos e-independent manner. Hydroxyl substitution at C-7 was required for in hibition of phenol hydroxylase activity independently of the oxidation potential. Glycosylation at either C-7 or C-3 was found to moderate t he inhibition of phenol hydroxylase activity. A linear relation was fo und between the degree of inhibition and the number of sugar residues for glycosylated flavanoids. There was no correlation between electroc hemical properties and effect on microsomal benzene hydroxylase activi ty.