Studies on the inhibition of ATP: Creatine phosphotransferase by NaCl

Abstract

Kinetic experiments have been undertaken to determine the apparent inhibition constants for the reaction of Cl − with various forms of creatine kinase. The conditions wer similar to those previously used for initial-velocity and isotope-exchange studies of the reaction. It has been shown that NaCl is a non-competitive inhibitor with respect to both substrates of the forward and reverse reactions. With the lower concentrations of the inhibitor used in studying the forward reaction, both the slopes and vertical intercepts of double-reciprocal plots as appeared to be linear functions of the concentration of NaCl. On the other hand, with the higher concentrations of NaCl used to inhibit the reverse reaction, the non-competitive inhibition was of the sloep-parabolic, intercept-linear type. From the values obtained for the apparent inhibition constants, it appears that Cl − may well react at sites on the enzyme at which substrate normally combines, and that the presence of a substrate on the enzyme affects the combination of Cl −. Whereas the interaction of Cl − with the ternary enzyme complex is very weak, two Cl − can react with free enzyme. The inhibition of the reaciton by sodium acetate is considerably less than that by NaCl.