Observations on the nature of bactracin A

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Abstract
Bacitracin A is a polypeptide containing the following amino-acid residues: cysteine, ornithine, lysine, histidine, aspartic acid, glutamic acid, phenylalanine, leucine and isoleucine. The wt. of the min. stoichiometric unit of bacitracin A HCl is about 1500. The latter contains 3 molecules of HC1 and one amide group. Electrometric titration and reaction with 1-fluoro-2, 4-dinitrobenzene indicate that the min. stoichiometric unit of bacitracin A contains the following ionizable groups: 2 carboxyls, one alpha-amino group, one histidine glyoxaline, and one delta-amino group of ornithine. The epsolon-amino group of lysine is not free. It is suggested that bacitracin A may be a cyclic polypeptide, in which a carboxyl group is condensed with the epsolon-amino group of lysine. Bacitracin A appears to contain no free thiol group or disulfide, but a thiol group is rapidly liberated when the peptide is treated with hot dilute acid. This group forms part of a cysteine residue. The liberation of the thiol group is accompanied by t he hydrolysis of an amide group and by the disappearance of an absorption max. in u.-v. at 254 m[mu]. On hydrogenolysis with Raney nickel the cysteine residue to bacitracin A is converted to an alanine residue whose alpha-amino group is free. Hydrolysis of the product of hydro -genolysis yields 2 new substances which give a blue color with ninhydrin. One of these substances, at least, is an amino alcohol. The possibiltiy that bacitracin A contains a thiazoline ring system is being considered.
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