The inhibition of catechol-O-methyltransferase by 2,3-dihydroxypyridine.

Despite its structural similarity to catechol, 2,3-dihydroxypyridine is not a substrate but a "dead-end" inhibitor of purified pig liver catechol-O-methyltransferase. It inhibits the methylation of 3,4-dihydroxyphenylacetic acid competitively with an inhibitor constant of 15 microM. Against the methyl donor, S-adenosyl-L-methionine, it is an uncompetitive inhibitor (Ki = 85 microM). Clearly, although 2,3-dihydroxypyridine interacts with the catechol-binding site of the enzyme, the presence of a nitrogen in the ring alters its susceptibility to O-methylation.