Kinetic analysis of enzymatic hydrolysis of ATP in human and rat blood serum.

Kinetic analysis of enzymatic hydrolysis of 14C- or 3H-labelled ATP was performed in the blood of healthy men donors and male Wistar rats. Nonspecific phosphatases were paralleled in blood serum by specific enzyme ATPase which is capable of dephosphorylating exogenous ATP in cooperation with other serum nucleotidases ultimately to adenosine. APparent Michaelis-Menten constant (Km) and maximal velocity (Vmax) values for rat serum ATPases are 68 +/- 7 microM and 7.0 +/- 0.3 nmoles ATP/mg protein per h, respectively. ATPase from human blood serum was characterized by lower respective Km and Vmax values: 39 +/- 5 microM and 2.5 +/- 0.2 nmoles ATP/mg protein per h. Activity of serum ATPase was decreased in the presence of membrane ecto-ATPase inhibitors PPADS and RB2, whereas the Na,K-ATPase inhibitor ouabain did not exert any inhibitory action on the measured enzyme activity.