Evidence from rat liver nuclear preparations that latency of microsomal UDP-glucuronosyltransferase is associated with vesiculation

Abstract

Nuclear, nuclear-envelope and microsomal preparations were prepared from rat liver, and their purity and morphology monitored by EM. UDP-glucuronosyltransferase activity in microsomal preparations, but not in standard nuclear or nuclear-envelope preparations, displays latency from the criterion of being enhanced (activated) by a range of detergents or the endogenous activator UDP-N-acetylglucosamine. Nuclear preparations resemble activated rather than native microsomal preparations in failing to transfer glucuronic acid from 4-nitrophenyl glucuronide to 2-aminophenol. EM indicates that membranes of nuclear preparations and of standard nuclear-envelope preparations remain, as in vivo, in a cisternal arrangement, whereas those of microsomal preparations are vesiculated. In nuclear-envelope preparations in which vesiculation was encouraged, the transferase can be activated by detergents. Latency of UDP-glucuronosyltransferase apparently results from vesiculation of membranes during preparation and the latency of the microsomal transferase is apparently largely a preparative artifact.