The effects of tunicamycin on protein glycosylation in mammalian and fungal systems.

By using membrane preparations from B. licheniformis, this enzyme has been assayed in both directions and found to be resistant to tunicamycin (1OOpg. ml-'). Therefore in wall-polymer assembly in B. licheniformis, B . subtilis and S . aureus tunicamycin has been shown to inhibit the biosynthesis of both peptidoglycan and the linkage units involved in the attachment of teichoic acids to peptidoglycan. Although in B. licheniformis a 5-fold difference was observed in the concentration of tunicamycin required to inhibit the two translocases, the known structural role of peptidoglycan points to inhibition of the synthesis of this polymer being responsible for the observed antibacterial activity. If, as suggested (Heifetz et al., 1979), tunicamycin acts as a substrate-product transition-state analogue binding irreversibly to sensitive enzymes, then the differences observed in the concentration of antibiotic required to inhibit the sensitive translocases in B. licheniformis may be a reflection of the affinity of tunicamycin for the two active sites. Finally, when considering the action of tunicamycin in terms of the experimental results obtained in bacteria, yeast and mammalian systems, the following common features become apparent. All the sensitive enzymes, with the possible exception of the one involved in the incorporation of N-acetylglucosamine into the linkage unit of M . luteus teichuronic acid (Rohr et al., 1977; Weston & Perkins, 1977), appear to involve the translocation of phospho-N-acetylglucosamine or its derivatives to a lipid acceptor. In this context phospho-N-acetylmuramoyl-pentapeptide can be regarded as a peptide-substituted 3-0-lactyl ether of Nacetylglucosamine. The amphipathic character of tunicamycin may be of major importance in the recognition of the polyprenyl phosphate acceptor in its membrane environment. Perhaps more surprising is the finding that, although the majority if not all of the sensitive enzymes catalyse the transfer of phosphorylated residues, tunicamycin itself does not contain phosphorus.