Demethylation in erythrocytes: a reaction involving hemoglobin

A reaction is described in erythrocytes of rat and of man whereby O-methylated metabolites of the catecholamines are demethylated to the corresponding catechols. The reaction was studied by incubating aliquots of erythrocyte lysates with radiolabeled O-methylated compounds and isolating the catechol product by alumina adsorption chromatography. The demethylating activity was located in the cytosol of the erythrocytes. Evidence was strong that oxyhemoglobin was responsible for the reaction: the demethylase activity was inseparable from oxyhemoglobin in several chromatographic separations. In addition, although commercially available hemoglobins were inactive in the reactions, after their conversion to oxyhemoglobin and purification, they did effect demethylation. Methemoglobin did not demethylate guaiacols and in fact inhibited demethylation by oxyhemoglobin. The reaction was inhibited by the addition of reduced pyridine nucleotides and of the methyl acceptor tetrahydrofolic acid.