5′-Fluorodeoxyadenosine synthase, a C-F bond-forming enzyme, has been purified from Streptomyces cattleya. The enzyme mediates a reaction between inorganic fluoride and S-adenosyl-L-methionine (SAM) to generate 5′-fluoro-5′-deoxy-adenosine. The molecular weight of the monomeric protein is shown to be 32.2 kDa by electrospray mass spectrometry. The kinetic parameters for SAM (K-m 0.42 mM, V-max 1.28 U/mg) and fluoride ion (K-m 8.56 mM, V-max 1.59 U/mg) have been evaluated. Both S-adenosyl-L-homocysteine (SAH) and sinefungin were explored as inhibitors of the enzyme. SAH emerged as a potent competitive inhibitor (K-i 29 muM) whereas sinefungin was only weakly inhibitory. (C) 2003 Published by Elsevier Science B.V. on behalf of the Federation of European Biochemical Societies.