BIOSYNTHESIS OF 5-HYDROXY-4-OXO-L-NORVALINE IN STREPTOMYCES-AKIYOSHIENSIS

The biosynthesis of 5-hydroxy-4-oxo-L-norvaline (HON) in Streptomyces akiyoshiensis has been investigated using C-13-labelled substrates. In corporations of C-13 label from sodium [1-C-13]-, [2-C-13]-, and [1,2- C-13(2)]acetate indicated that HON was formed from a four-carbon compo und derived from the citric acid cycle and the methyl carbon of acetat e. Feeding experiments using DL-[4-C-13]- and DL-[2-C-13,N-15]aspartat e demonstrated that aspartate served as the four-carbon precursor to H ON. Both enantiomers of aspartate were metabolized by S. akiyoshiensis , but the D isomer was consumed at a slower rate. The distribution of C-13 label in the intracellular L-glutamic acid isolated in these feed ing experiments is consistent with the operation of the citric acid cy cle in S. akiyoshiensis. A biosynthetic hypothesis that involves a con densation reaction between acetyl or malonyl CoA and the beta-carboxyl group of aspartate, and subsequent oxidative decarboxylation, is prop osed to account for the incorporation results. An analogous condensati on step has been proposed for the biosynthesis of other natural produc ts, including the carbapenem antibiotics. DL-[2-C-13,N-15]Aspartate wa s synthesized from [2-C-13]diethylmalonate and potassium [N-15]phthali mide via diethyl [2-C-13,N-15]phthalimidomalonate.