BIOSYNTHESIS OF FLUORINATED SECONDARY METABOLITES BY STREPTOMYCES-CATTLEYA

The biosynthesis of organofluorine compounds by Streptomyces cattleya NRRL 8057 was examined using F-19 NMR spectroscopy. The organism produ ced 1.2 mM fluoroacetate and 0.5 mM 4-fluorothreonine as secondary met abolites when cultured for 28 d on a chemically defined medium contain ing 2 mM fluoride. Cell suspensions from batch cultures harvested at t he growth maximum of 4 d were not capable of fluoride uptake or fluoro metabolite biosynthesis, but by 6 d had developed an efficient fluorid e-uptake system and biosynthesized the two fluorometabolites in almost equal proportions. As the harvest age increased, the proportion of fl uoroacetate to 4-fluorothreonine formed by cell suspensions rose progr essively so that 16-d-old cells showed a ratio of 76:26 for the two co mpounds. Fluoride uptake and fluorometabolite production by cell suspe nsions were highly dependent on pH, with both processes showing a maxi mum rate at pH 6.0 but declining rapidly at higher pH values. This dec rease was particularly marked in the case of fluoroacetate biosynthesi s which was barely detectable at pH 7.5. Fluoroacetate and 4-fluorothr eonine showed only low levels of interconversion by cell suspensions, suggesting that the carbon skeleton of neither was derived by metaboli sm of the other. The limited interconversion observed is explicable in terms of a small degree of biological defluorination occurring with e ach compound, followed by reincorporation of the resulting fluoride io n into the organic form by the active fluorinating system, a phenomeno n also noted on incubation of cell suspensions with a number of other fluorinated biochemical intermediates. Cell suspensions were supplemen ted with a variety of amino acids and tricarboxylic acid cycle interme diates to determine the identity of the carbon substrate of the fluori nating system. No compound tested significantly increased the total am ount of fluorometabolites formed or altered their relative proportions . However, in studies with C-14-labelled precursors, the highest level of incorporation into fluoroacetate by cell suspensions was recorded with [U-C-14]glycolate, suggesting that this compound or an activated derivative may be the substrate for the fluorinating system in the bio synthesis of fluoroacetate.