Adenosinetriphosphatase Activity of Human Serum

Abstract

In examining the adenosinetriphosphatase (ATP-ase) of human serum, a rather definite pH optimum was seen at certain acid values of pH. ATP was used as the Na salt. Serum from patients and healthy subjects was prepared from venous blood. ATP-ase was detd. in a system where the conc. of enzyme was the rate-determining factor. Five-tenths ml. of serum was added to 2.5 ml. of ATP soln. in 0.1 M veronal-HCl or acetate buffer at various values of pH. There was maximum activity with 3.38 and 9.67 micromoles of ATP at pH 8.9 and 4.8, respectively. After incubation at 37[degree]C for 1/2 to 2 hrs., the trichloracetic acid filtrate was analyzed for inorganic P. Controls with buffer and ATP or serum alone were used. Activity curves were obtained for the serum ATP-ase of a normal subject, a patient with cirrhosis, and a patient with metastatic prostatic carcinoma. The activity showed maxima in pHs between 8.7 to 9.1 and 4.6 to 5.1 in all sera studied. At pH 8.9, all 3 phosphate groups of ATP were hydrolyzed by normal and abnormal sera. Muscle adenylic acid was usually completely split under similar conditions. At pH 8.9, 0.29-0.32 micromole of adenylic acid was split. The corresp. values at pH 4.8 were less than 0.06 micromole, except for sera with elevated "acid" phenylphosphatase where the values were less than 0.18 micromole. There was no consistent relation between ATP-ase at pH 4.8 and "acid" phenyl-phosphatase. Quite high values of ATP-ase were often found in patients with bone and liver disease. The relative amts. of activity at pH 4.8 and 8.9 varied with different sera. More substrate was necessary at pH 4.8 for maximum activity. The evidence was suggestive of the view that the 2 ATP-ase optima represented different enzymes.