Biosynthesis of fluoroacetate and 4-fluorothreonine in Streptomyces cattleya. Incorporation of oxygen-18 from [2-2H,2-18O]-glycerol and the role of serine metabolites in fluoroacetaldehyde biosynthesis

Abstract

A series of isotope labelling experiments was carried out to investigate the biosynthesis of fluoroacetate and 4-fluorothreonine in resting cells of Streptomyces cattleya. Previous studies have shown that fluoroacetaldehyde is a precursor to both of these metabolites and the experiments were conducted to explore in greater detail the metabolic origin of fluoroacetaldehyde in S. cattleya. Ethanolamine and cysteamine are C2 metabolites of serine and cysteine respectively and these two metabolites emerged as candidate precursors to fluoroacetaldehyde in S. cattleya. However feeding experiments with [1,1-2H2]-ethanolamine and [1,1-2H2]-cysteamine did not indicate incorporation into the fluorometabolites, suggesting that these compounds are not relevant precursors to fluoroacetaldehyde in S. cattleya. Upon feeding [2-2H,2-18O]-glycerol to resting cells of S. cattleya, the deuterium atom was not incorporated into 4-fluorothreonine, however the oxygen-18 atom became incorporated into the carboxylate group of fluoroacetate and into the C(3)-O oxygen atom of 4-fluorothreonine. This observation indicates that there is an oxidation at C-2 of glycerol, but that the oxygen atom is formally retained from glycerol during the biosynthesis. In overview, the data suggest that fluoroacetaldehyde is derived from a C3 glycolytic intermediate rather than a C2 amino acid metabolite.