HEPATIC MONOACYLGLYCEROL ACYLTRANSFERASE ACTIVITY IN SUCKLING RATS

Abstract

Hepatic monoacylglycerol acyltransferase (MGAT) activity is 700-fold higher during the suckling period than in the adult rat. Specific activity in total particulate preparations rose from 9.4 nmol/min/mg before birth to a peak of 78 nmol/min/mg on the 6th postnatal day. MGAT activity fell sharply after day 8 and was 1.6 and 0.1 nmol/min/mg on day 28 and in adult rats, respectively. The activity had a pH optimum at 8.0 and was activated by albumin and by phospholipids. With (3H)palmitoyl-CoA and sn-2-monooleoylglycerol, more than 96% of the products were di- and triacylglycerols. 90% of the diacylglycerol product was the 1, 2 isomer. The activity was stable at 43° for 50 min and had t 1/2 values of 8 min and 4.5 min at 53.5 and 55°C, respectively. Suckling rat MGAT activities in liver and intestinal mucosa were 100- to 300-fold higher than in other tissues. MGAT activity was 12.5 fold greater with C16:0-CoA than with C8:0-CoA. Acetyl-CoA was not a substrate. The sn-2-monoacylglycerols were strongly preferred over the sn-1 isomers. No direct relationship was noted between monoacylglycerol chain length and apparent Km value. The presence of high MGAT activity suggests that the monoacylglycerol pathway provides a major route of glycerolipid synthesis in suckling rat liver.