Determination of differential activities of soluble and membrane-bound catechol-O-methyltransferase in tissues and erythrocytes

Catechol-O-methyltransferase (COMT) exists as two isoenzymes, a membrane-bo und form (MB-COMT) and a soluble form (S-COMT), with different roles in the metabolism of catecholamines and other catechol compounds. This report doc uments an HPLC assay for separate estimation of S-COMT and MB-COMT activity and examines activities of the two isoezymes among different rat tissues a nd in human and rat erythrocytes. Activities of MB-COMT and S-COMT varied w idely among tissues. There were higher activities of S-COMT than MB-COMT in all tissues except the adrenal medulla where MB-COMT was the predominant i soenzyme, consistent with the importance of this tissue and MB-COMT for the O-methylation of catecholamines. MB-COMT and S-COMT in rat and human eryth rocytes showed divergent levels acid patterns of activity. The assay repres ents a rapid and accurate method for quantifying MB-COMT and S-COMT in vari ous tissues and examining the relative roles of COMT isoenzymes in the meta bolism of catechol compounds in health and disease. (C) 1999 Elsevier Scien ce B.V. All rights reserved.