Localization of membrane-bound catechol-O-methyltransferase.

Previous studies of the distribution of catechol-O-methyltransferase (COMT) have concentrated on the soluble enzyme activity. In this study the activity of the membrane-bound enzyme was determined in different brain regions and peripheral tissues of the rat. Membrane-bound COMT, like the soluble enzyme, has a general distribution with high levels in liver, kidney, and vas deferens. However, the ratio of membrane-bound to soluble activity varies almost 30-fold in different tissues, with the highest ratio in brain. Membrane-bound activity varies twofold within brain. In view of their different localization and kinetic properties, it seems likely that the two forms of COMT have different functions in vivo.