Multiple effects of ions on ATP: l-arginine and ATP: Creatine phosphotransferases

Abstract

1. 1. Cations inactivate Sipunculus arginine kinase (mol. wt 84 000) (ATP: l-arginine phosphotransferase, EC 2.7.3.3). The order of increasing effectiveness is K +, NH 4 +, Li +, guanidinium cation, tetravalent spermine action. The action of lithium acetate and guanidine · HCl is expressed by a two-step inhibition: an initial immediate inhibition which is of the non-competitive type with respect to l-arginine and Mg 2+- ATP, and a slower inactivation. While the first stage can be observed at 10°C, the rate of the secondary one increases with temperature. This inhibition is similar to that observed with anions. The modification of the protein absorption spectrum which characterizes the action of anions is displayed with guanidine · HCl and spermine · 4HCl but not with K +, NH 4 +, Li +. 2. 2. The effects of KCl on Sipunculus arginine kinase in H 2O and in 2H 2O are qualitatively similar but quantitatively different. In 2H 2O the decrease of V by KCl is greater than in H 2O. However, the modification of the protein absorption spectrum is less sharp in 2H 2O than in H 2O. 3. 3. Rabbit muscle creatine kinase (ATP:creatine phosphotransferase, EC 2.7.3.2) shows a susceptibility towards anions and cations comparable to that of Sipunculus arginine kinase. The order of effectiveness of anions and cations on both enzymes is the same. The kinetic behaviour of the action of Cl − is identical for both enzymes. Nevertheless no modification of the protein absorbance spectrum is observed by the interaction of Cl −.