Mode of action of microbial bioactive metabolites.

Pathogenic microorganisms can be suppressed by cell wall destruction. Biosynthesis of peptidoglycans forming bacterial cell wall is interrupted by glycopeptides which inhibit polymerization of a disaccharide formed by N-acetylglucosamine and N-acetylmuramic acid, beta-lactams and their derivatives inhibit peptidoglycan cross-linking. Antibiotics inhibiting protein synthesis bind to different sites on the rRNA and interfere with the formation of the polypeptide chain. Tumor cells resistant to chemotherapeutic drugs overproduce proteins transporting the drugs out of cells; these proteins eliminate substances which inhibit transcription of transport proteins. Some antitumor drugs (anthracyclines, fluoroquinolones, acridines etc.) act at topoisomerases which irreversibly bind to DNA and inhibit DNA synthesis. Immunosuppressants affect various components of the immune system such as T-helper, T-effector cell function, antigen presentation and B-cell function. Antiparasitics--avermectins--bind to a receptor of this Gab-gated chlorine channel in the nerve fiber of nematodes and anthropodes, increasing the permeability of the membrane for chloride ions; the increased transport of chloride ions into the cell causes the death of the parasite. Ionophores dissolve in phospholipid bilayers and enormously increase their ionic permeability. Respiration inhibitors block the transport of electrons at several places of the respiratory chain. Rifamycin binds to the beta subunit of bacterial RNA polymerase, thereby blocking mRNA synthesis. Antiviral compounds inhibit the transcription of DNA by several mechnisms or by inhibition of viral entry into host cells.