Decavanadate inhibits catalysis by ribonuclease A

Pentavalent organo-vanadates have been used extensively to mimic the transi tion state of phosphoryl group transfer reactions. Here, decavanadate (V10O 286-) is shown to be an inhibitor of catalysis by bovine pancreatic ribonuc lease A (RNase A). Isothermal titration calorimetry shows that the K-d for the RNase A . decavanadate complex is 1.4 mu M. This value is consistent wi th kinetic measurements of the inhibition of enzymatic catalysis, The inter action between RNase A and decavanadate has a coulombic component, as the a ffinity for decavanadate is diminished by NaCl and binding is weaker to var iant enzymes in which one (K41A RNase A) or three (K7A/R10A/K66A RNase A) o f the cationic residues near the active site have been replaced with alanin e. Decavanadate is thus the first oxometalate to be identified as an inhibi tor of catalysis by a ribonuclease. Surprisingly, decavanadate binds to RNa se A with an affinity similar to that of the pentavalent organo-vanadate, u ridine 2',3'-cyclic vanadate. (C) 2000 Academic Press.