Polymyxin phenylalanine

The polymyxins—The members of the polymyxin group have very similar chemical and physical properties. They are all cyclic basic polypeptides containing characteristic constituents such as a,y-diaminobutyric acid, i,-threonine and a fatty acid. They differ by the presence or absence of the additional amino acids D-leucine, L-leucine, L-isoleucine, n-phenylalanine, D-valine and D-serine, as well as by the nature of the fatty acid Table 1.11). Their molecular weights are aU in the region of 1,200. Although several structural features had been established very early - the exact... 

The molecular weight of polymyxin B was shown by the method of partial substitution to be 1,150 d 10 per cent. Quantitative amino acid analysis yielded the amino acids a,y-diaminobutyric acid, L-threonine, D-phenylalanine and L-leucine in the molar proportions 6 2 1 1. Because no free a-carboxyl- and no free a-amino groups could be detected, polymyxin Bi had to be of a cyclic nature . Neither pepsin nor trypsin was found to attack the molecule and therefore partial hydrolysis and separation of the fragments was used for the elucidation of the structure. Of the 14 fragments isolated and identified, seven key peptides were necessary for proposing four tentative structures for polymyxin Two were formulated with a ring... 

Polymyxin B (C56H98Oi3Ni6 m.w.1202) is a cyclic peptide consisting for the major part of l-, < -, y-, diaminobutyric acid (5 residues), aside of L-threonine (2), L-leucine (1), D-phenylalanine (l),and (+)-6-methyl-octanoic acid (1). In order to be able to explain the formation of certain degradation products of this peptide it was first necessary to obtain some... 

Alanyl tryptophan ethyl ester pH 2.0 Alanyl tryptophan ethyl ester pH > 12.0 Alanyl phenylalanine ethyl ester pH 2.0 Polymyxine pH 2.0... 

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