ISOZYME-DEPENDENT SENSITIVITY OF ADENYLYL CYCLASES TO P-SITE-MEDIATEDINHIBITION BY ADENINE NUCLEOSIDES AND NUCLEOSIDE 3'-POLYPHOSPHATES

Recombinant adenylyl cyclase isozyme Types I, II, VI, VII, and three s plice variants of Type VIII were compared for their sensitivity to P-s ite-mediated inhibition by several adenine nucleoside derivatives and by the family of recently synthesized adenine nucleoside 3'-polyphosph ates (Desaubry, L., Shoshani, I., and Johnson, R. A. (1996) J. Biol. C hem. 271, 14028-14034). Inhibitory potencies were dependent on isozyme type, the mode of activation of the respective isozymes, and on P-sit e ligand. For the nucleoside derivatives potency typically followed th e order 2',5'-dideoxyadenosine (2',5'-ddAdo) > beta-adenosine > 9-(cyc lopentyl)-adenine (9-CP-Ade) greater than or equal to 9-(tetrahydrofur yl)-adenine (9-THF-Ade; SQ 22,536), with the exception of Type II aden ylyl cyclase, which was essentially insensitive to inhibition by 9-CP- Ade. For the adenine nucleoside 3'-polyphosphates inhibitory potency f ollowed the order Ado < 2'-dAdo < 2',5'-ddAdo and 3'-mono- < 3'-di- < 3'-triphosphate. Differences in potency of these ligands were noted be tween isozymes. The most potent ligand was 2',5'-dd-3'-ATP with IC50 v alues of 40-300 nM. The data demonstrate isozyme selectivity for some ligands, suggesting the possibility of isozyme-selective inhibitors to take advantage of differences in P-site domains among adenylyl cyclas e isozymes. Differential expression of adenylyl cyclase isozymes may d ictate the physiological sensitivity and hence importance of this regu latory mechanism in different cells or tissues.