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  • Title: Biosynthesis of the polyoxins, nucleoside peptide antibiotics: a new metabolic role for L-isoleucine as a precursor for 3-ethylidene-L-azetidine-2-carboxylic acid (polyoximic acid).
    Author: Isono K, Funayama S, Suhadolnik RJ.
    Journal: Biochemistry; 1975 Jul; 14(13):2992-6. PubMed ID: 1156577.
    Abstract:
    The biosynthetic origin of the carbon skeleton of 3-ethylidene-L-azetidine-2-carboxylic acid (polyoximic acid) is described. This unique cyclic amino acid is the C terminus of the nucleoside peptide antibiotics, the polyoxins, elaborated by Streptomyces cacaoi var, asoensis. In vivo experiments show that 14-C from [1-14-C]isoleucine, [U-14-C]isoleucine, [1-14-C]methionine, [U-14-C]methionine, [U-14-C]threonine, and [1-14-C]glutamate is incorporated into polyoximic acid; however, 14-C from [5-14-C]glutamate and [methyl-14-C]methionine is not incorporated. The distribution of 14-C in polyoximic acid clearly shows that the intact carbon skeleton of L-isoleucine is utilized directly. The incorporation of 14-C from [U-14-C]methionine, [U-14-C]threonine, and [1-14-CA1glutamate into polyoximic acid occurred only after their conversion to isoleucine via 2-ketobutyrate. A scheme is presented in which either of the two beta-unsaturated amino acids isolated from Bankera fuligineoalba, L-2-amino-3-hydroxymethyl-3-pentenoic acid or L-2-amino-3-formyl-3-penetenoic acid, is regarded as a possible intermediate amino acid between isoleucine and polyoximic acid.
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