Relationship between microsomal hydroxylase and glucuronyltransferase.

These experiments did not answer the question of whether one or several UDG-glucuronyltransferases are present in endoplasmic membranes of the liver. However, they present results which indicate that the glucuronlytransferase (s) have several properties in common with the hydroxylating cytochrome P-450 dependent enzyme system: the inducibility (which differs considerably after pretreatment with phenobarbital or 3-methylcholanthrene), the sex specificity, and the inhibition by the same compounds. The most obvious difference between the systems is the alteration of the enzyme activities after solubilization of the membranes by sonication or use of detergents.. On solubilization, the activity of the glucuronyltransferase (s) increases, whereas the opposite is true for the hydroxylating system which may lose one or several components essential for its activity (such as the NADPH dependent reductase). Our experiments can best be interpreted by assuming a common micro-environment around the enzymes produced by lipids and proteins which modulate both the rate of hydroxylation and that of glucuronyl-conjugation of drugs.