ISOFORM-SPECIFIC REGULATION OF ADENYLYL-CYCLASE BY OXIDIZED CATECHOLAMINES

Both epinephrine and manganese are known to stimulate cAMP production in cardiac homogenates. When added together, however, they inhibited a denylyl cyclase catalytic activity. Type V adenylyl cyclase, the major isoform in the heart, was also inhibited when an increasing concentra tion of epinephrine was added in the presence of manganese, Inhibition was not dependent on the condition of stimulation or preparation of t he enzyme. However, this inhibition was abolished in the presence of a nti-oxidant. Other catecholamines, including dopamine and isoprotereno l, as well as adrenochrome, an oxidized product of epinephrine, simila rly inhibited the activity of this enzyme. Kinetic analyses revealed t hat the K-m for the substrate ATP was unchanged, but the Vmax was sign ificantly decreased, In contrast, type II adenylyl cyclase, a non-card iac isoform, was resistant to such inhibition by adrenochrome and was somewhat stimulated by it, Thus, catecholamines, when oxidized, direct ly interacted with adenylyl cyclase in an isoform-specific manner in t he absence of G proteins. Our findings suggest that adenylyl cyclase i soforms have different sensitivity to various stresses, including oxid ative stress. (C) 1997 Academic Press Limited.