Inhibition of adenylate cyclase by polyadenylate

The effects of ribo- and deoxyribonucleic acids on the activity of detergent-dispersed adenylate cyclases from rat and bovine brain were examined. Mn2+ (10 mM)-activated adenylate cyclase was inhibited by micromolar concentrations of poly(A) (IC50 congruent to 0.45 microM). This inhibition was directly due to poly(A) and was not mediated by: (a) protein contamination of the poly(A) preparation, (b) metal chelation, (c) formation of an acid-soluble inhibitor of adenylate cyclase, (d) effects on the specific activity of [alpha-32P]ATP, (e) competition with MnATP for binding to adenylate cyclase, or (f) diversion of substrate to an alternate polymerase reaction. Inhibition of adenylate cyclase by poly(A) was on the enzyme's catalytic unit, as purified preparations of the enzyme from bovine brain were inhibited by poly(A). This inhibition by poly(A) was not likely mediated via the enzyme's "P"-site, through which activated forms of the enzyme are selectively inhibited by specific adenosine phosphates. In contrast with inhibition by the "P"-site agonist 3' AMP, inhibition of adenylate cyclase by poly(A) was slow in onset and was not reversible by dilution and showed a different metal-dependence. Inhibition of adenylate cyclase was relatively specific for poly(A) as poly(U) caused less than 50% inhibition and deoxyribonucleic acids had no effect. The potency and specificity of the inhibition of adenylate cyclase by poly(A) imply a biochemically interesting interaction that is possibly also of physiological significance.