Fatty acyl-coA and fatty acyl-acyl carrier protein as acyl donors in the synthesis of lysophosphatidate and phosphatidate in escherichia coli

Abstract

1. 1. A particulate fraction of Escherichia coli catalyzes the transfer of palmitate from palmityl-CoA and palmityl-acyl carrier protein to sn-glycero-3-phosphate. When a series of long-chain acyl thiolesters including myristyl-, palmityl-, palmitoleyl- and cis-vaccenyl-CoA and acyl carrier protein were tested in the acylation of sn-glycero-3-phosphate, the palmitate esters were the most effective substrates. 2. 2. Lysophosphatidate has been identified as the initial product formed from sn-glycero-3-phosphate and either palmityl-CoA or palmityl-acyl carrier protein. The lysophosphatidate can either be acylated to phosphatidic acid or be dephosphorylated to the monoglyceride. The extent to which both reactions occur depends on experimental conditions and on the nature of the acyl donor. 3. 3. Phosphatidic acid synthesis from sn-glycero-3-phosphate was observed in the presence of saturated or unsaturated CoA esters. 4. 4. When palmityl-acyl carrier protein was the only acyl donor present, hardly any phosphatidate was synthesized and the main products were lysophosphatidate and monoglyceride. In the additional presence of unsaturated acyl-acyl carrier protein phosphatidate was formed. This indicates the possibility of phosphatidate biosynthesis from sn-glycero-3-phosphate and acyl-acyl carrier protein esters. 5. 5. The acylation of 1-acyl- sn-glycero-3-phosphate by acyltransferases from E. coli occurred preferentially with unsaturated fatty acyl thiolesters. Especially, acyl-acyl carrier protein esters were used with great selectivity for the acyl portion in this acylation reaction. 6. 6. The palmitate thiolester of 4'-phosphopantetheine was not used as acyl donor to sn-glycero-3-phosphate under conditions in which acyl thiolesters of both CoA and acyl carrier protein are active. 7. 7. Some properties of the enzyme catalyzing the dephosphorylation of lysophosphatidate and phosphatidate are described.