The acylation of lysophosphatidylglycerol in rat heart: evidence for both in vitro and in vivo activities

Abstract

The reacylation of lysophospholipids back to their parent molecules is important for attaining the appropriate fatty acyl composition in many phospholipids and for preventing the accumulation of arrhythmia generating lysophospholipids in the heart. In this study, we report the presence of an active acyltransferase activity for lysophosphatidylglycerol reacylation to phosphatidylglycerol in rat heart membrane preparations. The activity of acyl-Coenzyme A:1-acylglycerophosphorylglycerol acyltransferase in rat heart subcellular fractions was in the order of microsomal > mitochondrial > cytosol. The activity in the membrane fractions were characterized and found to have a pH optimum in the alkaline range. However, significant enzyme activity was observed at physiological pH. With oleoyl-Coenzyme A as substrate, the microsomal activity had a preference for lysophosphatidylglycerol substrates in the order of myristoyl > palmitoyl > oleoyl > stearoyl. The apparent K m values for 1-palmitoylglycerophosphorylglycerol and oleoyl-Coenzyme A were 9.4 and 7.1 μM. respectively. In contrast, the mitochondrial activity had a preference for lysophosphatidylglycerol substrates in the order of oleoyl > myristoyl = stearoyl = palmitoyl. The apparent K m values for 1-oleoylglycerophosphorylglycerol and oleoyl-Coenzyme A were 17.8 and 18.0 μM, respectively. Both membrane activities were heat labile as pre-incubation at 55° for 1 min completely abolished the activity. However, pre-incubation at 50°C resulted in different profiles of inactivation in both microsomal and mitochondrial fractions. Both membrane activities were inhibited by high concentrations of lysophosphatidylglycerol and affected to a similar extent by various detergents. To demonstrate whether reacylation of lysophosphatidylglycerol to phosphatidylglycerol occurred in vivo, isolated rat hearts were perfused for 60 min in the Langendorff mode with 0.1 μM 1-palmitoylglycerophosphoryl[ 14C]glycerol bound to albumin. 1-Palmitoylglycerophosphoryl[ 14C]glycerol was readily taken up by the isolated perfused rat heart and significant synthesis of phosphatidyl[ 14C]glycerol was observed. The findings indicate the presence of an acyl-Coenayme A:1-acylglycerophosphorylglycerol acyltransferase activity in the rat heart subcellular membranes which is capable of catalyzing lysophosphatidylglycerol acylation to phosphatidylglycerol in vitro and in vivo.