INHIBITION OF ENZYMATIC DEGRADATION OF RNA BY BOUND CALCIUM AND MAGNESIUM

1. The effect of Ca2+ and Mg2+ on bovine pancreatic ribonuclease (ribonucleate pyrimidine-nucleotido-2′-transferase (cyclizing), EC 2.7.7.16) activity was reinvestigated with highly polymerized yeast RNA at I 0.11 and pH 7.0. Both Ca2+ and Mg2+ had an inhibitory effect at concentrations of 0.01 mM to 10.0 mM. At the point of 50% enzyme inhibition, Ca2+ was about 50 times more effective than Mg2+ on a mole per mole basis. 2. Both Ca2+ and Mg2+ are competitive inhibitors of ribonuclease. Ca2+ and Mg2+ appear to inhibit the initial nonhydrolytic action of ribonuclease. 3. Ca2+ binding to RNA was estimated by measuring the decrease at 470 mμ when RNA was added to a Ca2+-murexide solution at pH 7.0. Over a concentration range of 0.01 mM to 10.0 mM, Ca2+ binding increased to about one Ca2+ bound for every 3 nucleotide pairs at 3 mM Ca2+ and decreased markedly at higher Ca2+ concentrations. 50% enzyme inhibition occurred when one Ca2+ was bound for every 40 nucleotide pairs. © 1969.