Biosynthetic routes of molecular species of lung phosphatidylglycerol

Rat lung phosphatidylglycerol contained about 21% of saturated species, a predominant of which was dipalmitoyl. The biosynthetic features of molecular species of the phospholipid were investigated by incubating rat lung slices with radioactive precursors. The labeling profiles of molecular species of phosphatidylglycerol by [2-3H]glycerol and [1-14C]palmitate were significantly different from that of diacylglycerol and phosphatidylcholine. Mono- and dienoic species of phosphatidylglycerol were shown to have extremely high reactivity with [3H]glycerol, but the labeling of saturated species were almost half of the saturated diacylglycerol. The rate of [14C]palmitate incorporation was significantly lower in the saturated species of phosphatidylglycerol as compared to that in diacylglycerol and phosphatidylcholine. It was also noted that the lung tissue can utilize 1-[1-14C] palmitoyl lysophosphatidylglycerol to form tetraenoic and polyenoic phosphatidylglycerol by the direct acylation and saturated phosphatidylglycerol probably by the transacylation. The data indicate that the saturated species of phosphatidylglycerol may be synthesized de novo via phosphatidic acid CDP-diacylglycerol route and also via transacylation pathway, but it may not be synthesized by the direct acylation pathway.