Fluoroacetate distribution, response to fluoridation, and synthesis in juvenile Gastrolobium bilobum plants

Like angiosperms from several other families, the leguminous shrub Gastrolobium bilobum R.Br. produces and accumulates fluoroacetate, indicating that it performs the difficult chemistry needed to make a C-F bond. Bioinformatic analyses indicate that plants lack homologs of the only enzymes known to make a C-F bond, i.e., the Actinomycete flurorinases that form 5'-fluoro-5'-deoxyadenosine from S-adenosylmethionine and fluoride ion. To probe the origin of fluoroacetate in G. bilobum we first showed that fluoroacetate accumulates to millimolar levels in young leaves but not older leaves, stems or roots, that leaf fluoroacetate levels vary >20-fold between individual plants and are not markedly raised by sodium fluoride treatment. Young leaves were fed adenosine-¹³C-ribose, ¹³C-serine, or ¹³C-acetate to test plausible biosynthetic routes to fluoroacetate from S-adenosylmethionine, a C₃-pyridoxal phosphate complex, or acetyl-CoA, respectively. Incorporation of ¹³C into expected metabolites confirmed that all three precursors were taken up and metabolized. Consistent with the bioinformatic evidence against an Actinomycete-type pathway, no adenosine-¹³C-ribose was converted to ¹³C-fluoroacetate; nor was the characteristic 4-fluorothreonine product of the Actinomycete pathway detected. Similarly, no ¹³C from acetate or serine was incorporated into fluoroacetate. While not fully excluding the hypothetical pathways that were tested, these negative labeling data imply that G. bilobum creates the C-F bond by an unprecedented biochemical reaction. Enzyme(s) that mediate such a reaction could be of great value in pharmaceutical and agrochemical manufacturing.