Enhancement of microsomal 1-ACYL-Sn-Glycero-3Phosphocholine acyltransferase activity in rat submandibular gland during postnatal growth

Phosphatidylcholine (PC) in mammalian cells has been gathering much attention as not only a major component of membrane bilayers but also a precursor of functional lipids such as diacylglycerol, eicosanoids, and platelet activating factor. Among the many enzyme reaction steps for the biosynthesis of PC, the specific activities of these enzymes have been shown to be altered during cell growth. Previously, we demonstrated the marked changes in the specific activity and the substrate specificity of 1 -acyl-sn-glycero-3-phosphocholine acyltransferase (1-acyl-GPC ATase) in rat submandibular and parotid glands the growth of which was proliferated by chronic administration of 0-adrenergic agonist. Membrane phospholipid biosynthesis may be enhanced during the postnatal growth of rat salivary glands and the maturation of receptor-linked secretory function may extensively develop 3 weeks after birth. Therefore, we examined the effects of postnatal growth on 1 -acyl-GPC ATase activity in the rat salivary glands. The wet weight of submandibular gland increased three fold in the rats from 3 to 9 weeks old. The microsomal 1 -acyl-GPC ATase activity in 10-week-old rats was 2- to 4-fold higher than that in 3-week-old rats. In this enhancement of specific activity, not K_m values but the acyl-CoA selectivity was changed: the enzyme in the mature rats became more preferable to 20:4- and 20:5-CoAs. However, the specific activities of this enzyme in the parotid gland and liver were hardly changed during the growth. These findings suggest that tissue-specific enhancement of 1 -acyl-GPC ATase activity occurs due to the induction of its protein, which may play a specific role in the submandibular gland.