Thiosulfate sulfurtransferase and UDP-glucuronosyltransferase activities in cholestatic rat liver induced by common bile duct ligation

Abstract

We have investigated the effect of cholestasis on the hepatic thiosulfate sulfurtransferase (rhodanese) and UDP-glucuronosyltransferase (UDP-GT) activities in rats. Rhodanese activities in the liver cytosol, mitochondria and microsomal fractions as well as in the rat serum, and UDP-GT activity in the microsome have been investigated for a period of 42 days after common bile duct (CBD) ligation. The cytosolic rhodanese activity showed a significant decrease between the first through the 42nd day, and the mitochondrial activity showed a significant decrease between the 7th through the 42nd day after CBD ligation compared to the activities from the sham operated control, respectively. In the case of microsomal preparation, both rhodanese and UDP-GT also showed significant decrease in their activities after the ligation for the former enzyme between the 14th and the 42nd days, and for the latter enzyme between the third and 42nd days, respectively. On the other hand, the serum rhodanese activity increased markedly soon after the ligation, exhibiting the peak activity after 1 day of CBD ligation with about 4.6-fold increment. The activity subsequently decreased gradually reaching to the control level at the 42nd day post-ligation. Enzyme kinetic parameters of hepatic rhodanese and UDP-GT were analyzed using sodium thiosulfate and pnitrophenol as substrates, respectively, with the preparations from the 28th day post-ligation. The results indicated that although the Km values of these enzymes were about the same as the sham-operated control, the Vm a x values of the both enzymes decreased s i g n i f i c a n t l y. These results, therefore, suggest that the biosynthesis of rhodanese and UDP-GT have been reduced in response to cholestasis, and that the elevation of rhodanese activity in the serum is most likely due to leakage from the liver subsequent to CBD ligation. Keywords: thiosulfate sulfurtransferase (rhodanese), UDP-glucuronosyltransferase, cholestatic rat liver