KINETIC-ANALYSIS OF ENZYMATIC-HYDROLYSIS OF ATP IN HUMAN AND RAT-BLOOD SERUM

Kinetics analysis of enzymatic hydrolysis of C-14- or H-3-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 c ooperation with other serum nucleotidases ultimately to adenosine. App arent Michaelis-Menten constant (K-m) and maximal velocity (V-max) val ues for rat serum ATPases are 68 +/- 7 mu M and 7.0 +/- 0.3 nmoles ATP /mg protein per h, respectively. ATPase from human blood serum was cha racterized by lower respective K-m and V-max values: 39 +/- 5 mu M 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 an d RB2, whereas the Na,K-ATPase inhibitor ouabain did not exert any inh ibitory action on the measured enzyme activity.