Activities of lipid reesterifying enzymes in jejunal microsomes of bile fistula rats attempts to correlate enzyme activities with microsomal phospholipid content

Abstract

1. 1. Microsomes from control and bile fistula rat jejuna were assayed for specific and total activities of acyl-CoA synthetase (acid:CoA ligase (AMP) EC 6.2.1.3) and acyl-CoA:monoglyceride acyltransferase. In addition, measurements of microsomal phospholipid content were performed. In certain groups of rats the classes of micro-somal phospholipid were quantitated. 2. 2. Specific and total enzyme activities were found to be reduced in bile fistula rats as previously observed. Enzyme activities were restored to normal levels in bile fistula rats by infusing sodium taurocholate and lecithin at concentrations of 7.5 and 2 mM, respectively. Infusion of 7.5 mM sodium taurocholate alone resulted in some increase in enzyme specific activities toward the normal range. Values for total enzyme activities were actually normal under these conditions. Infusion of greater concentrations of bile salts and/or lecithin was not as effective in maintaining normal enzyme activities. 3. 3. Phospholipid content of microsomes was decreased in bile fistula rats. This change was found to be the result of reduced recoveries of lecithin. Intraduodenal infusion of moderate amounts of sodium taurocholate (7.5 mM) and lecithin (2 mM) restored microsomal phospholipid content to normal. It was also observed, however, that this could be accomplished by infusing 7.5 mM sodium taurocholate without lecithin into bile fistula rats. It is concluded, therefore, that under the conditions of this study the presence of lecithin in the intestinal lumen is not essential for the maintenance of normal amounts of phospholipid of jejunal microsomes. 4. 4. Microsomal enzyme activity was generally normal when microsomal phospholipid content was found to be normal and was abnormal when phospholipid levels were depressed. Statistical analysis showed a correlation existed between enzyme specific activities and phospholipid content. It was not definitely established, however, whether changes in microsomal phospholipid composition directly influenced microsomal enzyme activities or whether changes in enzyme activities and phospholipid levels merely vary in the same direction in response to changes in the amount of fat being absorbed by the intestine under different experimental conditions.