Tyrocidines, Gramicidin

There are relatively few chemotherapeutic drugs which cause permeability increases in membranes such as the antifungal polyenes and the antibacterial circular oligopeptides of the tyrocidin, gramicidin and polymyxin families. Most of these are too toxic for systemic use but polymyxins have been given systemically in severe Pseudomonas infections with an attending risk of renal toxicity. 

Organism Amphomycin Bacitracin Tyrothricin Gramicidin Tyrocidine Gramicidin S Colistin Polymyxin B Viomycin... 

In their similar action on the cell membrane the tyrocidines, gramicidins and the polymyxins resemble other surface active agents. Like these, they contain also lipophilic and lipophobic groups, which, as has been revealed by studies on gramicidins, may be separated in the molecule by being fixed on different sides of the molecular plane. 

Antibiotics. The genes involved in the synthesis of a variety of antibiotics have been isolated (34,35). These include antibiotics such as erythromycin, streptomycin, and also peptide antibiotics such as gramicidin and tyrocidin. Characterization of these gene products facUitates the design of novel antibiotics. In addition, overexpression of some of these gene products is also expected to improve the yield of the antibiotic (34,35). 

In 1939 the isolation of a mixture of microbial products named tyrotbricin from a soil bacillus was described. Further investigation showed this material to be a mixture of gramicidin and tyrocidine. In rapid succession the isolation of actinomycin (1940), streptothricin (1942), streptomycin (1943), and neomycin (1949), produced by Streptomjces were reported and in 1942 the word antibiotic was introduced. Chloramphenicol, the first of the so-called broad spectmm antibiotics having a wide range of antimicrobial activity, was discovered in 1947. Aureomycin, the first member of the commercially important tetracycline antibiotics, was discovered in 1948. 

Although tyrothricia is too toxic for parenteral therapy, it was formerly sold in the United States as oral lo2enges. Modem tyrothricin formulations are composed of 70—80% tyrocidines and 30—20% linear gramicidins. Tyrocidines are not as active as linear gramicidins and are too toxic for any therapeutic use by themselves. The bactericidal linear gramicidins are used in the United States solely as an ophthalmic solution in combination with polymyxin B sulfate and neomycin sulfate. The linear gramicidin is used in this aqueous product as a substitute for bacitracin, which lacks stabiUty under such conditions. 

Tyrocidine [8011-61-8] is a mixture of three closely related components. Tyrocidine studies on mechanism of action (98), biosynthesis on multien2yme complexes (93,99,100), and chemistry (101) are available, and tyrothricin production is discussed (102). Although the mechanism of action of linear gramicidins has been well researched, such work on tyrocidine is more limited it appears that tyrocidine damages membranes (103,104). 

Gramicidin is a peptide antibiotic first isolated by Dubos in 19391 as a crude complex together with a second peptide antibiotic known as tyrocidin. The mixture of the two antibiotics was called tyrothricin. Although the mixture was discovered about ten years after penicillin2, tyrothricin was the first antibiotic utilized in clinical practice. 

Ivashkiv has used this reaction to assay gramicidin and tyrocidine in fermentation broth155. The antibiotics are... 

Bartley and coworkers separated gramicidin from tyrocidine using Sephadex LH20199. 

Lipmann, F., Gevers, W., Kleinkauf, H., and Roskoski, R. Jr. (1971). Polypeptide synthesis on protein templates the enzymatic synthesis of gramicidin S and tyrocidine. Adv. Enzymol. Relat. Areas Mol. Biol. 35, 1-34. 

In 1939, Rene Dubos, Waksman s former postdoctoral student, extracted two chemicals, tyrocidine and gramicidin, from the soil germ Bacillus brevis. These chemicals cured bacterial infections in cattle but were too toxic for humans. This discovery prompted a number of scientists to expand the search for microbes in the soil, microbes capable of making chemicals that could kill disease-causing bacteria in humans. 

Major classes of antibiotics include more than 200 peptides such as the gramicidins, bacitracin, tyrocidines and valinomycin (Fig. 8-22)k more than 150 penicillins, cephalosporins, and related compounds tetracyclines (Fig. 21-10) the macrolides, large ring lactones such as the erythromycins (Fig. 21-11) and the polyene antibiotics (Fig. 21-10). 

Our approach has been essentially empirical in nature with less emphasis on the theoretical. We have isolated single substances, proved their purity, and determined their covalent structure by classical methods of organic chemistry we have then used these substances of molecular weight ranging from 1,000 to 14,000 as model solutes for the study of conformation and intermolecular interaction. Solutes of special interest have been gramicidin SA (2), bacitracin A (3), polymyxin B, and the tyrocidines A, B, and C (4). All are cyclic antibiotic polypeptides. The first three behave in aqueous solution as reasonably ideal solutes and do not associate, but the tyrocidines associate strongly and are interesting models for the study of association phenomena. Other model solutes of... 

Circulin A Fungisporin Gramicidin S Malformin A(, C Mycobacillin Polymixin Bi Tyrocidine A, B Valinomycin... 

Early work summarized in Sec. I.B had shown that ACV is made from L-Aad, L-Cys, and L-Val, that 5-(L-a-Aad)-L-Cys (AC) may be converted into ACV, but L-Cys-D-Val is not converted. Likewise, D-Val is not a substrate for ACV synthetase, contrary to the first-characterized NRPS systems of gramicidin S and tyrocidine [2,3], These observations are in agreement with the scheme, except for the incorporation of AC. This dipeptide was later shown to be activated as an adenylate. 

David, S.A., Balaram, P., Mathan, V.I. Interaction of basic amphiphilic polypeptide antimicrobials, gramicidin S, tyrocidin and efrapeptin, with endotoxic lipid A. Med Microbiol Lett 2 (1993) 42-47. 

F. Lipmann (1971). Gramicidin S and tyrocidine biosynthesis primitive process of sequential addition of amino acids on polyenzymes . In R. Buvet and C. Ponnamperuma (Eds), Molecular Evolution, Vol. 1, Chemical Evolution and the Origin of Life, North-Holland, Amsterdam, The Netherlands, p. 381. 

The catalytic mechanisms and molecular recognition properties of peptide synthetases have been studied for several decades [169]. Nonribosomal peptides are assembled on a polyenzyme-protein template, first postulated by Lipmann [170]. The polyenzyme model was refined into the thiotemplate mechanism (Fig. 11) in which the amino acid substrates are covalently bound via thioester linkages to active site sulfhydryls of the enzyme and condensed via a processive mechanism involving a 4 -phosphopantetheine carrier [171-173].The presence of a covalently attached pantetheine cofactor was first established in a cell-free system that catalyzed enzymatic synthesis of the decapeptides gramicidin S and tyrocidine. As in the case of fatty acid synthesis, its role in binding and translocating the intermediate peptides was analyzed [174,175]. 

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