Tyrocidine composition

New York) and challenged to find a soil microbe that could destroy a bacteria. ° In 1939, he discovered a substance extracted from a soil bacillns. Tyrothricin (later showed composition of two substances, gramicidin (20%) and tyrocidine (80%), cured mice infected with pnenmococci. It was the first natural antibiotic extracted from soil bacteria, able to arrest the growth of staphylococcns, bnt proved highly toxic. 

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). 

Another homeomeric basic cyclic peptide was isolated in 1943 by Gause and Brazhnikova (220) from different strains of B. brevis. This peptide, relatively easily isolated, was called Gramicidin S., and is very close, in properties and composition, to the tyrocidine group. Hence it will be discussed with this family of peptides. 

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