The Biosynthesis and Turnover of Surfactant Lecithin and Protein

Abstract

The pathways involved in the biosynthesis of lecithin have been studied in lung tissue. In vivo and in vitro data support the hypothesis that surfactant lecithin is synthesized in situ via the cytidine diphosphate (CDP)-choline pathway. The data turther suggest that the enzymes involved in methylation of phosphatidyl-ethanolamine to lecithin are not active. Also, the presence of phosphatidyl-N,N-dimethylethanolamine (PDME) in lung tissue cannot be attributed to bacterial contamination. The biological half-life for choline and palmitate incorporated into lecithin is 43 and 16 hours, respectively, the latter suggesting acyl exchange. The biological half-life of leucine incorporated into the protein of surfactant is 45 hours. The similarity in biological half-life for choline and leucine suggests that surfactant is a lipoprotein which turns over as a single unit.