Butyrate metabolism in streptomycetes. Characterization of an intramolecular vicinal interchange rearrangement linking isobutyrate and butyrate in Streptomyces cinnamonensis
The incorporations of various carbon-13 and deuterium labelled forms of isobutyrate into the polyether antibiotic monensin-A have provided evidence for the existence of a novel rearrangement in whole cells of Streptomyces cinnamonensis, which leads to the conversion of isobutyrate into butyrate. This rearrangement is shown to proceed in an intramolecular fashion by migration of the carboxy carbon of isobutyrate to the 2-pro-S methyl, with a concomitant back migration of a hydrogen atom from this methyl group predominantly into the 3-pro-R position in butyrate. Formally, therefore, the carboxy carbon is replaced with overall retention of configuration, in a vicinal interchange rearrangement. The significance of these observations with regard to the coenzyme requirements of the rearrangement, and its relationship to polyether and macrolide antibiotic production in Streptomycetes is discussed.