K +-dependent phosphatase activity observed in the presence of both adenosine triphosphate and Na +

Abstract

Listen

Translate article

1. 1.Addition of both ATP and Na + caused a remarkable increase in the activity of the K +-dependent phosphatase at low concentrations of K +, although addition of either ATP or Na + alone was inhibitory. The apparent K m for K + decreased from 2 mM to p.2 mM on addition of both substances. The υ max was depressed by them. 2. 2.CTP, ITP, and ADP showed effects similar to ATP in the presence of Na +. The optimal concentrations of ATP and ADP were observed to be 10 −4 M and 2 · 10 −4 M, but that of CTP and ITP was 10 −3 M. AMP, 3′,5′-cyclic AMP, CDP, UTP, and GTP had no significant stimulatory effect. 3. 3.Replacement of Na + with other monovalent cations, such as Rb +, NH 4 +, Cs +, or Li +, caused the stimulatory effect of ATP to disappear. 4. 4.The K +-dependent phosphatase became heat labile on addition of K +, but was stabilized by further addition of Na + and ATP. 5. 5.Ouabain inhibited the K +-dependent phosphatase activity more in the presence of ATP and Na + than in their absence. 6. 6.The K +-dependent phosphatase activity was less sensitive to treatment with F − in the presence of ATP and Na + than in their absence. 7. 7.From these results it was concluded that the affinity of the K +-dependent phosphatase for K + was increased by addition of ATP and Na +, and the properties came closer to those of the (Na +-K +)-ATPase.