Wheat flavoneO-methyltransferase catalyzes three sequential methylations of the flavone tricetin. Like other flavonoidO-methyltransferases, the pro-tein is a homodimer. We demonstrate, using analytical ultracentrifugation, that perchlorate dissociates the dimer into monomers. The resulting mono-mers retain all their catalytic capacity, including the ability to catalyze the three successive methylations.