Peptides homeomeric

Peptides containing just amino acids (often the less common amino acids) are called homeomeric peptides, and peptides containing other compounds are heteromeric peptides or peptoids. This group includes ... 

These terms, homeomeric peptides and heteromeric peptides, should not be confused with the terms, homopeptide and heteropeptide, which Blout and Linsley (77) used to designate peptides consisting respectively of a single type of amino acid or of several different types of amino acids. 

The discovery of tyrocidine was made by Hotchkiss and Dubos (286) who, in 1940 isolated a polypeptidelike substance (287) from tyrothricin, an extract of B. brevis cultures. This substance, called tyrocidine by them, is insoluble in acetone and ether. An excellent review of Hotchkiss (284) discusses the work done up to 1944 on the extraction, purification, structure, and biological properties of tyrocidine. The work from 1944 to 1949 is discussed by Synge (575). Actually, tyrocidine, as it was described in the early work, is not a single peptide, but is a family of basic homeomeric peptides, certain of which are cyclic, related one to the other, and characterized by the possession of ornithine. 

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. 

Nisin is a substance consisting of a mixture of at least two homeomeric peptides. Mattick and Hirsch (406) in 1947 obtained nisin from cultures of a strain of Streptococcus lactis, which exhibits remarkable antibiotic activity with respect to S. agalactiae. It is obtained in the following manner (64). 

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