Peptides, antibiotic heteromeric

The polymyxins are antibiotic, basic, heteromeric peptides, which are active only against Gram-negative bacteria. They all contain L-a,Y-diaminobutyric acid, L-threonine, and (4-)6-methyloctanoic acid (55,114,... 

The peptide circulin, which was isolated from a culture of Bacillus circulans (431) should be placed in the polymyxin group. This antibiotic, active preferentially on Gram-negative bacteria (430) is a cyclic, basic heteromeric peptide, containing, as do polymyxins, L-a,7-diaminobutyric acid, threonine, and an optically active isomer of pelargonic acid which is probably (-b)6-methyloctanoic acid. In addition, circulin contains D-leucine (458). The composition (Table IX) of circulin is close to that of polymyxins A and E. However, this antibiotic, unlike polymyxin A, is inactivated by the enzyme lipase (458). Paper chromatography (173) distinguishes circulin from polymyxins A and E. 

Park and Johnson (452) showed that acid-labile phosphorylated compounds accumulated in the cells of S. aureus H treated with low concentration of penicillin. Park (446) then isolated three nucleotides of uridine, possessing as a common basic unit uridine-5 -diphosphate, attached to an amino sugar (449). One of these nucleotides also possessed a peptide chain linked to the amino sugar, therefore a heteromeric peptide. This nucleotide-peptide was later isolated from antibiotic untreated staphylococci (447), in much lower yield. 

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