[Nonspecific phosphodiesterases of human leukocytes, blood platelets and serum]

Phosphodiesterases from blood cells and serum can be subdivided in several groups according to substrate specificity, optimum pH and effects of inhibitors: 1) Acidic phosphodiesterase activities were not inhibited by EDTA, represented the whole p3'T hydrolysing activity, but only a part of the activity hydrolysing the other substrates (p5'T was not hydrolysed at acidic pH). This acid phosphodiesterase activity was high in white blood cells and platelets but very low in serum. 2) Neutral phosphodiesterase activity was prevalent in leucocytes when BpP and BMP were used as substrates. 3) Alkaline phosphodiesterase activity was characterized by substrate specificity at optimum pH and distribution in cells and serum: in serum there are phosphodiesterases hydrolysing all checked substrates (p3'T excepted) at optimum pH 9.0, whereas in blood cells alkaline phosphodiesterase activities are very low for all substrates (excepted for p Phi Pn and p5'T). In each cell and serum we have determined, for all phosphodiesterase activities, the linearity of activity of versus time and versus protein concentration, the effect of substrate and effector concentration and the heat stability.