Tyrocidine hydrolysis

When the last condensation reaction has occurred, the linear precursor needs to be released from the enzyme. For this important last step, several mechanisms are known simple hydrolysis of the thioester (balhimycin, vancomycin), intramolecular cyclization leading to a lactam (tyrocidine, bacitracin) or a lactone (surfactin), or even reductive thioester cleavage (linear gramicidin). In some cases, the linear precursor is dimerized (gramicidin S) or even trimerized (bacillibactin, enterobactin) before cyclization (Fig. 2). Even though these reactions are critical for the compound s bioactivity, the catalytic domains responsible for the release are not found in all NRPS systems and will therefore be called modifying domains. 

The molecular weight of tyrocidine A was found to be about 1,270 . Total hydrolysis and quantitative amino acid analysis revealed the exact composition . Partial hydrolysis, fractionation of the resulting peptide mixture by countercurrent distribution, ion-exchange chromatography and paper-chromatography, followed by sequential analysis, led Paladini and Craig to the structure of tyrocidine A see Table 1.6). 

Thus Synge and Tiselius (1947) were able to fractionate the components of tyrocidin, both by elution and displacement methods. In a study of the partial hydrolysis of ovalbumin Moring-Claesson (1948) was able to separate by adsorption the unchanged protein from the breakdown products. The former was adsorbed much more strongly on alumina and less strongly on carbon than the smaller peptides and amino acids. 

Christensen (221) has used p-toluene sulfonyl chloride on the polypeptide tyrocidine, and after hydrolysis has isolated oxy-] -toluene sulfonyltyrosine. 

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