ON INITIAL STAGE IN PEPTIDOGLYCAN SYNTHESIS .3. KINETICS AND UNCOUPLING OF PHOSPHO-N-ACETYLMURAMYL-PENTAPEPTIDE TRANSLOCASE (URIDINE 5'-PHOSPHATE)

The initial reaction in the biosynthesis of peptidoglycan is catalyzēd by phospho-N-acetylmuramyl-pentapeptide translocase (uridine diphosphate-N-acetylmuramyl-L-Ala-D-γ-Glu-L-Lys-D-Ala-D-Ala: C55-isoprenoid alcohol phosphate phospho-N-acetylmuramyl-pentapeptide transferase) according to the reaction uridine diphosphate-N-acetylmuramyl-pentapeptide + acceptor phosphate [formula omitted] acceptor diphosphate-N-acetylmuramyl-pentapeptide + uridine monophosphate where acceptor is C55-isoprenoid alcohol. The kinetics of transfer are characterized by a biphasic reaction when uridine monophosphate is measured (k1 = 0.018 min-1; k2 = 1.8 × 10-8 M min-1). The formation of acceptor diphosphate-N-acetylmuramyl-pentapeptide is characterized by pseudo-first-order kinetics (k1 = 0.018 min-1). With the liberation of uridine monophosphate in the second phase, there is a corresponding formation of phospho-N-acetylmuramyl-pentapeptide. On the basis of the kinetic evidence, the formation of an enzymephospho-N-acetylmuramyl-pentapeptide intermediate in the transfer to C55-isoprenoid alcohol phosphate is proposed. In addition to the transfer reaction, the enzyme catalyzes the exchange of uridine monophosphate with the uridine monophosphate moiety of uridine diphosphate-N-acetylmuramyl-pentapeptide. The ratio of the exchange rate to the transfer rate varies from 6 to 24. Thus, the transfer of phospho-N-acetylmuramyl-pentapeptide from the proposed enzyme intermediate to lipid acceptor phosphate is the rate-limiting step. Dodecylamine inhibits the synthesis of lipid acceptor diphosphate-N-acetylmuramyl-pentapeptide (Ki = 6.5 × 10-4 M) and causes the release of phospho-N-acetylmuramyl- pentapeptide. The effects of various surfactants on the exchange and transfer reactions are described and interpreted on the basis of the proposed model for the transfer of phospho-N-acetylmuramylpentapeptide from UDP-N-acetylmuramyl-pentapeptide to lipid acceptor-phosphate. © 1969, American Chemical Society. All rights reserved.