Studies on the biosynthetic pathways of molecular species of lecithin by rat lung slices.

Abstract

The metabolic heterogeneity of rat lung lecithin was studied by incubation of lung slices with various radioactive precursors. The results are summarized as follows: 1. 1. Using [3H]glycerol and [14C]palmitate, the ratio of 14C/3H was much higher in lecithin than in either phosphatidic acid or diglyceride, suggesting that palmitate is incorporated into lecithin by pathways other than the de novo synthesis via phosphatidic acid and diglyceride. 2. 2. The high specific activity was found in dienoic species with [3H]glycerol and with [14C]choline, in saturated species with [14C]palmitate, and in hexaenoic species as well as dienoic species with [3H]methionine. 3. 3. With lysolecithin labeled with [3H]glycerol and [14C]choline, a higher specific activity of polyenoic species than of oligoenoic species was found. A similar behavior of both isotopes indicated that intact glycerylphosphorylcholine was incorporated. 4. 4. With lysolecithin labeled with [3H]glycerol and [14C]palmitate at Position 1, a relatively higher incorporation into saturated species of 14C activity than of 3H activity was observed. The incorporation of 14C activity was found both in Position 2 (40%) and in Position 1 (60%). The data suggest that a transacylation between two molecules of lysolecithin can be a principal pathway for the formation of saturated lecithin species in lung.