Oxidation of palmitoyl-carnitine by mitochondria isolated from human term placenta

Abstract

It has been shown that slices prepared from either 13–14 week or term human placental tissue are able to oxidize palmitic acid as measured by collecting the evolved 14CO 2 from [1- 14C]palmitic acid (1,2). It has also been shown by Norum (3) that mitochondria isolated from this organ contain considerable amounts of carnitine palmitoyl transferase (EC 2.3.1.23) activity. This finding suggests that this enzyme plays a role in fatty acids oxidation by these mitochondria. To our knowledge fatty acids oxidation by mitochondria isolated from human term placenta has not yet been studied. This communication reports data indicating that isolated mitochondria from human term placenta oxidize palmitoyl-carnitine at the rate about 50% of the rate of isocitrate oxidation. Palmitic acid and palmitoyl-CoA alone were not oxidized under conditions examined. Palmitoyl-CoA in the presence of carnitine was oxidized at the rate about 50% of palmitoyl-carnitine oxidation. Palmitic acid in the presence of ATP, CoA, and carnitine was oxidized at the same extent as palmitoyl-CoA plus carnitine. The data obtained suggest that the formation of palmitoyl-carnitine is the rate limiting step in palmitoyl-CoA oxidation by human term placental mitochondria.