Complex lipid synthesis in hamster intestine

1. Three enzymes engaged in complex lipid synthesis, diglyceride acyltransferase, cholinephosphotransferase and lysolecithin acyltransferase were studied in nonfasting hamster intestinal mucosa. 2. The specific activities of diglyceride acyltransferase and lysolecithin acyltransferase were greatest in the proximal intestine in villous tips correlating with the physiological and morphological site of lipid absorption. The specific activity of cholinephosphotransferase did not vary either between tip and crypt preparations or in the proximal as compared to the distal intestine. 3. When comparison was made between the 2 pathways of lecithin synthesis studied, the specific activity of lysolecithin acyltransferase was 2-3-fold greater than cholinephosphotransferase in villous tips, no difference was observed in crypts. The data suggests that, in villous tips, lecithin is predominately synthesized via the lysolecithin acyltransferase pathway and, in toto, the enzymatic studies further suggest that it is this pathway which provides the lecithin associated with intestinal triglyceride transport. 4. Competition for the common substrate, diglyceride, in villous tips was examined by determining the specific activities of diglyceride acyltransferase and cholinephosphotransferase using either an aqueous dispersion of diglyceride or microsomal membrane bound diglyceride synthesized from glycerol 3-phosphate. In each instance, triglyceride was the predominant reaction product suggesting that diglyceride, in villous tips, is chiefly distributed into the triglyceride synthetic pathway.