Acylation of sn-glycerol 3-phosphate in Escherichia coli. Study of reaction with native palmitoyl-acyl carrier protein.

The sn-glycerol-3-phosphate acyltransferase activity of Escherichia coli has been assayed using native palmitoyl-acyl carrier protein as the acyl donor. This substrate was synthesized by a plant chloroplast system which utilized E. coli acyl carrier protein. The properties of the acyltransferase as assayed with palmitoyl-acyl carrier protein were similar to those observed using palmitoyl-CoA as the acyl donor. This finding suggested that single enzyme catalyzed transfer of acyl groups from either thioester to sn-glycerol 3-phosphate. This hypothesis was tested by assay of two classes of E. coli mutants which have altered sn-glycerol-3-phosphate acyltransferases. Both classes (plsA and plsB) of mutants have similarly altered activities as assayed with either palmitoyl-acyl carrier protein or palmitoyl-CoA. These results indicate that the same acyltransferase enzyme (or enzyme system) catalyzes the incorporation of both thioester substrates into phospholipid. Other experiments have shown that the acyltransferase of a plsB mutant was abnormally thermolabile only when palmitoyl-CoA was the acyl donor in the reaction. No thermolability was observed with palmitoyl-acyl carrier protein as acyl donor. The thermolability observed with palmitoyl-CoA is attributed to the detergent properties of this substrate. In agreement with Lueking and Goldfine (Lueking, D. R., and Goldfine, H. (1975) J. Biol. Chem. 250, 4911-4917), we found that guanosine-5'-diphosphate-3'-diphosphate (ppGpp) inhibits the acyltransferase only when palmitoyl-CoA was the acyl donor. No inhibition was observed when the acyltransferase was assayed with palmitoyl-acyl carrier protein in the presence of ppGpp. Incubation of the enzyme with ppGpp to assay results in a profound inhibition of acyltransfer from palmitoyl-CoA but has no effect on the incorporation of acyl groups from palmitoyl-acyl carrier protein.