Chloramphenicol glucuronyl transferase: Assay, ontogeny and inducibility

A sensitive and specific assay has been developed for the measurement of chloramphenicol glucuronyl transferase (CGT) activity. This activity has been quantified in crude rat liver preparations and localized to the microsomal fraction. The apparent Km and Vmax for chloramphenicol (at 5.0 mM uridine diphosphoglucuronic acid) are 0.40 mM and 1129 pmol/min/mg of protein, respectively, and the apparent Km and Vmax for uridine diphosphoglucuronic acid (at 20.0 mM chloramphenicol) are 4.67 mM and 790 pmol/min/mg of protein, respectively. Several activators of other glucuronyl transferases have little or no effect on chloramphenicol glucuronyl transferase. Chloramphenicol glucuronyl transferase activity is detectable in crude rat liver preparations on the 17th day of gestation and rises slightly prenatally and rapidly postnatally. Adult levels are reached by the 10th postnatal day. The activity of CGT in crude rat liver preparations is considerably enhanced by prior in vivo administration of phenobarbital, suggesting induction of the enzyme. The homozygous Gunn rat has normal or elevated levels of CGT in crude liver preparations in spite of this strain's markedly diminished ability to glucuronidate bilirubin. This suggests a genetic difference between CGT and bilirubin glucuronyl transferase and is evidence in favor of a multiplicity of enzymes catalyzing the addition of glucuronic acid to various aglycones.