Microcalorimetric study of the system adenosine-5′-triphosphate—sodium, potassium adenosine-5′-triphosphatase: Part 1. Determination of the catalytic activity of Na +, K + ATPase

Abstract

The catalytic activity of adenosine-5′-triphosphatase (5′-ATPase), activated by Na + and K + ions in the presence of Mg 2+ ions, was determined by a direct method using batch microcalorimetry. The enzymatic hydrolysis of 5′-ATP in Tris—HCl buffer was used without any auxiliary reaction. The rate of heat change associated with the enzymatic reaction, which could be related to the enzymatic activity of the Na +, K + ATPase, gave rise to a linear correlation between the calorimetric output and the enzymatic activity. The method was successfully applied to real matrices, in particular to membranes of human erythrocytes, without particular pretreatment.