Involved in the biosynthesis of fluorometabolites. Catalyzes the formation of a C-F bond by combining S-adenosyl-L-methionine (SAM) and fluoride to generate 5'-fluoro-5'-deoxyadenosine (5'-FDA) and L-methionine. It can also use 2'-deoxyadenosine in place of adenosine as substrate. fluoride + S-adenosyl-L-methionine = 5'-deoxy-5'-fluoroadenosine + L-methionine Competitively inhibited by S-adenosyl-L-homocysteine (AdoHcy) and S-adenosyl-L-homocysteine (SAH). Sinefungin is only weakly inhibitory. kcat is 0.07 sec(-1) for 5'-FDA synthase activity with SAM as substrate(at pH 7.9 and 37 degrees Celsius). kcat is 0.06 sec(-1) for 5'-FDA synthase activity with fluoride as substrate (at pH 7.9 and 37 degrees Celsius). Optimum temperature is 55 degrees Celsius. Homohexamer; dimers of trimer. Belongs to the SAM hydrolase / SAM-dependent halogenase family.