Gramicidin molecular weight

Hodgkin28 examined crystals of gramicidins A and B by x-ray diffraction. She estimated that the molecular weight of gramicidin A was approximately 3800, Previous estimates by chemical methods were approximately 7000. In 1953, Cowan and Hodgkin29 published a second report on gramicidin B. 

The diffusion constants for the gramicidin complex were determined in acetic acid and ethanol solution75. The molecular weight range of gramicidin was calculated as 2800-5000. 

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... 

Measurement of the molecular weight gave an approximate value of 1300. On this basis, what is the molecular formula of Gramicidin S ... 

The antibiotics from B. brevis are of much higher molecular weight and presumably are of more complicated structure. Tyrothrycin was the original solid active material from the culture but it was soon shown to be a mixture. Gramicidin was crystallized from the mixture by the appropriate solvents. From the mother liquor tyrocidine was crystallized. 

Fig. 10. Mass spectra of from MALDIMS, and from ESIMS. For MALDIMS the mass scale was calibrated with myoglobin ions as an internal standard. For ESIMS the mass scale was calibrated externally using the doubly charged and singly charged ions of gramicidin S. The right hand panel of the ESIMS spectrum shows the deconvoluted spectrum, giving measured molecular weights for the mtgor species, which differ by one hexose. Deviations from the calculated values are shown in parentheses.

Doubling reactions , in which two molecules of the activated peptide condense prior to cyclization, have been observed on several occasions, and have been used for the synthesis of gramicidin S . Because of these side-reactions, the careful characterization of the end-products, especially the determination of the molecular weights, is of paramount importance. 

The longest peptide synthesized by a non-ribosomal mechanism in vitro is alamethicin which is a nonadecapeptide (9). The biosynthesis of alamethicin is initiated on the synthetase by acetylation of thiol-ester-bound aminoisobutyric acid, which remains enzyme bound. Acetvl-CoA serves as the acetate donor. Activation and elongation reactions seem to follow the biosynthesis mechanism of gramicidin S on a multienzyme complex with a molecular weight of approx. 480 000. Alamethicin biosynthesis is terminated by attachment of ohenvlalaninol. which is probably the reaction product of a separate enzyme (107i... 

Ivanov, V. T., Sychev, S. V. The Gramicidin A Story in Structure of Complexes Between Biopolymers and Low Molecular Weight Molecules (Snatzke, G., Bartmann, W., eds.), Wiley, New York 1982, p. 107... 

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