Phospholipid substrate-specificity of the L-serine base-exchange enzyme in rat liver microsomal fraction

The specificity of the L-serine base-exchange enzyme towards the fatty acid composition of the phospholipid substrate was investigated with a rat liver microsomal fraction. The relative rates of L-serine incorporation into saturated-hexaenoic, saturated-pentaenoic, saturated-tetraenoic, saturated-trienoic, dienoic-dienoic, monoenoic-dienoic, saturated-dienoic and saturated-monoenoic + saturated-saturated phosphatidylserine molecular species were 42, 5, 23, 4, 5, 4, 5 and 11% respectively. This is similar to, but not identical with, the relative mass abundance of these molecular species in total liver cell phosphatidylserines. The results indicate that the substrate-specificity of the L-serine base-exchange enzyme can at least in part explain the observed fatty acid composition of rat liver phosphatidylserines.