DETECTION OF ACYL-COA-BINDING PROTEIN IN HUMAN RED-BLOOD-CELLS AND INVESTIGATION OF ITS ROLE IN MEMBRANE PHOSPHOLIPID RENEWAL

Acyl-CoA-binding protein (ACBP) has been identified in a number of tis sues and shown to affect the intracellular distribution and utilizatio n of acyl-CoA. We have detected ACBP in the cytosol but not the membra ne of human red blood cells and, using an e.l.i.s.a. with antibodies p repared against human liver ACBP, found that its concentration was 0.5 mu M. To investigate the role of ACBP in human red blood cells, we ad ded purified human liver ACBP and radiolabelled acyl-CoA to isolated m embranes from these cells, ACBP prevented high concentrations of acyl- CoA from binding to the membrane but could not keep the acyl-CoA in th e aqueous phase at low concentrations. This suggested the presence of a pool in the membrane with a binding affinity for acyl-CoA that was g reater than that of ACBP for acyl-CoA. In the presence of lysophosphol ipid, this membrane-bound pool of acyl-CoA was rapidly used as a subst rate by acyl-CoA: lysophospholipid acyltransferase (LAT) to generate p hospholipid from lysophospholipid. We also found that ACBP-bound acyl- CoA was preferred over free acyl-CoA as a substrate by LAT. These resu lts are the first documentation that human red blood cells contain ACB P and that this protein can affect the utilization of acyl-CoA in plas ma membranes of these cells. The interactions between acyl-CoA, ACBP a nd the membrane suggest that there are several pools of acyl-CoA in th e human red blood cell and that ACBP may have a role in regulating the ir distribution and fate.