Initial membrane reaction in peptidoglycan synthesis. Interaction of lipid with phospho-N-acetylmuramyl-pentapeptide translocase.

The initial membrane reaction in the biosynthesis of peptidoglycan is catalyzed by phospho-N-acetylmuramyl (MurN Ac)-pentapeptide translocase (UDP-MurNAc-Ala-gamma DGlu-Lys-DAla-DAla undecaprenyl phosphate phospho-MurNAc-pentapeptide transferase). In addition to the transfer reaction, the enzyme catalyzes the exchange of [3H]uridine monophosphate with the uridine monophosphate moiety of UDP-MurN Ac-pentapeptide. Two distinct discontinuities are observed in the slopes of the Arrhenius plots of the exchange and transfer activities at 22 and 30 degrees C for the enzyme from Staphylococcus aureus Copenhagen. Anisotropy measurements of perylene fluorescence and electron spin resonance measurements of N-oxyl-4',4'-dimethyloxazolidine derivatives of 12- and 16-ketostearic acid intercalated into membranes from this organism define the lower (T1 = 16--22 degrees C) and upper (Th = 30 degrees C) boundaries of a phase transition. These values correlate with the discontinuities observed for the activity measurements. Thus, it is proposed that the physical state of the lipid micro-environment of phospho-MurNAc-penetapeptide translocase has a significant effect on the catalytic activity of this enzyme.