Photolabeling acyl CoA binding proteins in microsome preparations

To identify key enzymes that participate in acylglycerol metabolism, 12-[(5-iodo-4-azidosalicyl)amino]dodecanoyl-coenzyme A (ASACoA) was employed as a photoaffinity label for those enzymes that use fatty acyl CoA as a co-substrate. ASACoA inhibited diacylglycerol acyltransferase activity in liver microsomes and was incorporated into triacylglycerol in a microsome dependent reaction. When photoactivated, ASACoA labeled four proteins in rat liver (75, 54, 50 and 37 kDa) and in epididymal fat cell (75, 64, 54 and 37 kDa) microsomes. Photolabeling was sensitive to palmitoyl CoA. After solubilization in Triton X-114, all four proteins were concentrated into the detergent phase, indicating that they are integral membrane proteins.