RECOGNITION OF THE LIPID INTERMEDIATE FOR ARABINOGALACTAN ARABINOMANNAN BIOSYNTHESIS AND ITS RELATION TO THE MODE OF ACTION OF ETHAMBUTOL ON MYCOBACTERIA

Despite major advances in our understanding of the structure of mycoba cterial cell walls, little is known of their biogenesis, and yet they are the site of action of many anti-tuberculosis drugs and implicated in much of the pathology of tuberculosis and leprosy. A family of mono glycosyl polyprenylphosphates was isolated from Mycobacterium smegmati s, containing arabinose, ribose, and mannose. The isoprenoid nature of the lipid components was established by H-1 NMR, and fast atom bombar dment mass spectroscopy (FAB-MS) demonstrated the presence of C-50 dec aprenyl-P derivatives and smaller amounts of the C-35 octahydroheptapr enyl-P products. The configuration of the mycobacterial decaprenol was established as mono-trans, octa-cis, pointing to carriers of unusual structure. Combined gas chromatography (GC)/MS, FAB-MS/MS, and H-1 MMR allowed characterization of one of the primary components as beta-D-a rabinofuranosyl-1-monophosphodecaprenol. Pulse chase metabolic labelin g of cells with D-[C-14]glucose indicated that the decaprenyl-P-arabin ose is an active intermediate in the biosynthesis of the arabinan of c ell wall arabinogalactan and arabinomannan. The identification of poly -prenyl-P-ribose suggests the existence of ribose containing polysacch arides in the cell walls of M. smegmatis or/ and of a novel epimerase in the D-arabinose biosynthetic pathway. Ethambutol, a powerful anti-t uberculosis drug known to inhibit arabinogalactan and arabinomannan bi osynthesis, results in the rapid accumulation of decaprenyl-P-arabinos e, indicating that the drug interferes with either the transfer of ara binose from the donor or, alternatively, the synthesis of the arabinos e acceptor itself.