Mammals express nine membranous adenylyl cyclase isoforms (ACs 1–9), a structurally related soluble guanylyl cyclase (sGC) and a soluble AC (sAC). Moreover,Bacillus anthracisandBacillus pertussisproduce the AC toxins, edema factor (EF), and adenylyl cyclase toxin (ACT), respectively. 2′(3′)-O-(N-methylanthraniloyl)-guanosine 5′-[γ-thio]triphosphate is a potent competitive inhibitor of AC in S49 lymphoma cell membranes. These data prompted us to study systematically the effects of 24 nucleotides on AC in S49 and Sf9 insect cell membranes, ACs 1, 2, 5, and 6, expressed in Sf9 membranes and purified catalytic subunits of membranous ACs (C1 of AC5 and C2 of AC2), sAC, sGC, EF, and ACT in the presence of MnCl2.N-Methylanthraniloyl (MANT)-GTP inhibited C1·C2 with aKiof 4.2 nm. Phe-889 and Ile-940 of C2 mediate hydrophobic interactions with the MANT group. MANT-inosine 5′-[γ-thio]triphosphate potently inhibited C1·C2 and ACs 1, 5, and 6 but exhibited only low affinity for sGC, EF, ACT, and G-proteins. Inosine 5′-[γ-thio]triphosphate and uridine 5′-[γ-thio]triphosphate were mixed G-protein activators and AC inhibitors. AC5 was up to 15-fold more sensitive to inhibitors than AC2. EF and ACT exhibited unique inhibitor profiles. At sAC, 2′,5′-dideoxyadenosine 3′-triphosphate was the most potent compound (IC50, 690 nm). Several MANT-adenine and MANT-guanine nucleotides inhibited sGC withKivalues in the 200–400 nmrange. UTP and ATP exhibited similar affinities for sGC as GTP and were mixed sGC substrates and inhibitors. The exchange of MnCl2against MgCl2reduced inhibitor potencies at ACs and sGC 1.5–250-fold, depending on the nucleotide and cyclase studied. The omission of the NTP-regenerating system from cyclase reactions strongly reduced the potencies of MANT-ADP, indicative for phosphorylation to MANT-ATP by pyruvate kinase. Collectively, AC isoforms and sGC are differentially inhibited by purine and pyrimidine nucleotides.
Purification and some properties of an IMP-specific 5′-nucleotidase from yeast
