Some Properties of Metal Ion-independent Adenosine Triphosphatase from Dog Kidney

Abstract

A new type of ATPase [EC 3.6.1.3], which is independent of metal ions, was previously purified from dog renal cortex. Using the highly purified enzyme (specific activity: 25 μmoles P1 released/mg protein·min), the effects of various reagents on the activity were studied. The molecular weight of the enzyme was estimated to be approximately 55,000. The activity was inhibited to 40% at pH 6.2 and 37° in the presence of 1 mM ascorbate. The ascorbate inhibition was neutralized by histidine, imidazole, arginine, or creatinine; these reagents somewhat stimulated the activity. The ascorbate inhibition was markedly increased in the presence of 10 μM Cu2+, which by itself did not affect the activity. This increased inhibition was also completely neutralized in the presence of histidine, imidazole, arginine, or creatinine. The activity was completely inhibited by 20 μM N-bromosuccinimide. This inhibition was also neutralized by histidine, imidazole, arginine, or creatinine. Enzyme activity previously inactivated by ascorbate was partially restored by adding histidine or arginine, but enzyme activity previously inactivated by N-bromosuccinimide was not restored. Neither histidine nor creatinine neutralized inhibition by ADP or ATP. Histidine and imidazole did not change the Km value of the enzyme for ATP, though they increased the Vmax value of the enzyme.