The submicrosomal distribution of hepatic uridine diphosphate glucuronyltransferases in the rabbit

Abstract

1. Rabbit liver microsomes were subfractionated into rough- and smooth-surfaced types, and glucuronyltransferase activity in each microsomal subfraction was determined with p-nitrophenol, o-aminophenol and phenolphthalein as substrates. The glucuronyltransferase activity measured with p-nitrophenol and o-aminophenol as substrates was localized predominantly in rough-surfaced microsomes. Glucuronyltransferase measured with phenolphthalein as substrate was equally present in rough- and smooth-surfaced microsomes. 2. Phenobarbital pretreatment of rabbits did not stimulate any of the glucuronyltransferase activities measured in either rough- or smooth-surfaced microsomes. 3. Preincubation of rabbit liver microsomes for 30-60min. at 37 degrees under oxygen did not cause any loss of glucuronyltransferase activity. Such preincubation caused either no change or increased enzyme activity in both submicrosomal fractions. The relative distribution of transferase activity in rough- and smooth-surfaced microsomes was not affected by preincubation.

Hepatic Aminopyrine N-Demethylase System: Further Studies of Assay Procedure

“…Since the product measured (formaldehyde) is identical for each reaction, apparent activity of aminopyrine N-demethy lation should decrease when both substrates exist in the reaction mixture (39). Gram et al reported the inhibition of N-demethylation of 4-monomethylaminoantipyrine by amino pyrine (40), which supports the above assumption. Interaction of two substrates with the same site of cytochrome P-450 could account for the decrease of formaldehyde production with incubation time (Fig.…”

Hepatic and Intestinal Drug-Metabolizing Enzymes and the Tissue Distribution and Excretion of 14C-7,12-Dimethylbenz[a]anthracene in Rats Fed Diets Varying in Fat Concentration

“…Benzo[a]pyrene hydroxylase (BPH) assays were made according to Nebert and Gelboin [20] and employed standard so lutions of 3-hydroxybenzo[a]pyrenc and quinine sul fate for monitoring the sensitivity and accuracy of spectrofluoromctric measurements. Uridine-5'-diphosphoglucuronic acid transferase (UDPGA trans ferase) activity was assayed according to Gram et al [21] with p-nitrophcnol as the substrate.…”

TCDD-Induced Changes in Rat Liver Microsomal Enzymes

“…Microsomes were pelleted by centrifugation of the postmitochondrial supernatant at 105000 g for 70 min, washed once with HEPES-KCI buffer, and finally resuspended in HEPES so that 1.0 ml of microsomal suspension contained material from 0.5g liver (wet weight). Smooth-and rough-surfaced endoplasmic reticulum (SER and RER) fractions were prepared by homogenizing chopped liver sections in 0.25M sucrose (pH 7.0) and preparing the microsomal subfractions on discontinuous sucrose gradients by the procedure of Gram et al (9), 10 ml of postmitochondrial supernatant and 12 ml of 1.3-M sucrose being used. Liver mitochondria were prepared by the procedure of Nelson et al (10) and resuspended in 0.25M sucrose so that 2.0 ml of suspension contained mitochondria from 3.Og liver (wet weight).…”