These in vitro tests may prove valuable to screen potential tumor growth promoters.

In guinea pig heart homogenate, 34% of both choline and ethanolamine phosphoglycerides were in the form of plasmalogens (1-alkenyl, 2-acyl glycerophospholipid). Plasmalogens accounted for 39% of the choline phosphoglycerides and 36% of the ethanolamine phosphoglycerides in the mitochondrial fraction. Ethanolamine plasmalogen was the major ethanolamine phosphoglyceride (63%) in the guinea pig heart microsomal fraction. A high arachidonyl content was found in both diacyl and 1-alkenyl, 2-acyl glycerophosphoethanolamine. The C-2 fatty acyl profiles of the diacyl and 1-alkenyl, 2-acyl choline phosphoglycerides differed considerably from each other in the homogenate as well as in the subcellular fractions. Significant differences in the C-2 fatty acyl profiles also were observed in diacyl and 1-alkenyl, 2-acyl ethanolamine phosphoglycerides. Such differences suggest there is no direct metabolic relationship between the diacyl glycerophosphocholine (-ethanolamine) and its plasmalogen analog.

The importance of the deacylation-reacylation pathway for attaining the desired fatty acid composition in microsomal phospholipids has been well established. It is not clear, however, whether this mechanism is of equal importance in mitochondria. The absence of acyltransferase activity in mammalian heart mitochondria has been reported in a number of studies. In the present study we report the presence of acyltransferase activities for lysophosphoradylglycerocholines in guinea-pig heart mitochondria. This enzyme showed properties that were considerably different from those of the microsomal enzymes. Of all the acyl-CoAs tested (C18:0, C18:1, C18:2 and C20:4) the mitochondrial enzyme utilized only linoleoyl-CoA as fatty acyl donor and utilized both 1-acyl-sn-glycero-3-phosphocholine and 1-alkenyl-sn-glycero-3-phosphocholine as fatty acyl acceptors. The presence of significant quantities of fatty acids other than linoleate at the C-2 position of mitochondrial acylglycerophosphocholines, coupled with the specificity of the enzyme for linoleoyl-CoA, suggest that, in addition to reacylation, other mechanisms play a significant role in producing the molecular composition of these phospholipids found in the mitochondria.

No abstract

Ethanolamine glycerophospholipids of mammalian heart mitochondria have a high content of arachidonic acid. Since the presence of acyltransferases that acylate 1-radyl glycerophosphoethanolamine had not been reported in the organelle, it was not known whether this high arachidonate content could be attained by the deacylation-reacylation pathway. In this study we have detected the presence of acyl-CoA:1-acyl-glycerophosphoethanolamine acyltransferase and acyl-CoA:1-alkenyl-glycerophosphoethanolamine acyltransferase activities in the guinea pig heart mitochondria. Both acyltransferases were active with palmitoyl-, stearoyl-, oleoyl-, linoleoyl-, and arachidonoyl-CoAs, but the highest activities were obtained with arachidonoyl-CoA. The acyl-CoA specificities of the enzyme(s) did not reflect the fatty acid composition of the ethanolamine glycerophospholipids. The utilization of arachidonoyl-CoA by these acyltransferases in the guinea pig heart mitochondria suggests that these enzymes may play a significant role in contributing to the high arachidonate content of the ethanolamine glycerophospholipids. However, mechanisms beyond the acyl specificity of the reacylation reactions are also involved in the maintenance of the overall acyl composition of the ethanolamine glycerophospholipid in the cardiac mitochondria.