Polymyxins composition

Dunnick and O Leary [149] examined the lipid composition of a number of bacteria both sensitive and resistant to polymyxin and tetracycline. All fatty acid extracts from antibiotic resistant Gramnegative organisms contained higher concentrations of cyclopropane acids than the corresponding extracts from sensitive organisms. Thus, cyclopropane acids and unsaturated fatty acids appear to play a role in the integrity of the penetration barrier at least for polymyxin and tetracycline. 

Table 1.11. Comparative amino acid and fatty acid composition of the polymyxins ... 

Recently it has been reported that polymyxin Bj differs from polymyxin Bj only in the replacement of the ( + )-6-methyloctanoic acid by 6-methylheptanoic acid . Polymyxin A and C are only known in their qualitative, and polymyxin D and M > only in their quantitative amino acid composition Table 1.11). Polymyxin M is at present being studied intensively " . 

Table IX (326,541) summarizes the amino acid composition of the various polymyxins. 

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. 

Hausmann, W., and L. C. Craig Polymyxin B. Fractionation, molecular weight determination, amino acid and fatty acid composition. J. Am. Chem. Soc. 76, 4892 (1954). 

Khoklov, a. S., and C. C. Chi Determination of the amino acid composition of polymyxin M by the method of counter-current distribution. Biokhimiya 26, 296 (1961). 

SiLAEV, A. V., V. M. Stepanov, E. P. Yulikova, E. V. Troshko, and E. D. Levin Chemistry of polymyxin M. I. Qualitative amino acid composition and analysis of end groups. Zhur. Obshchei Khim. 31, 297 (I96la). 

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