Localization of Membrane‐Bound Catechol‐O‐Methyltransferase

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Abstract
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.