The properties of plasma membrane bound adenosine deaminase(ADase) from human placenta have been investigated.
The enzyme exhibits a broad pH optimum from pH 6 to 8 and is heat labile, being completely inactivated by heat treatment at 70°C for 10 minutes.
The enzyme is not effected at pH 7 by 2 mM. Li+, Mg²+, Ca²+, Mn2+, Co²+, Fe²+ and
Zn2+, while the enzyme is activated by 2 mM Ca2+ and Co²+ at pH 8 and inhibited by 2 mM Cu2+ independent of pH.
The enzyme activity is completely recovered by EDTA (4 mM) only in case of adding Cult after preincubation of enzyme with substrate.
The apparent Michaelis constant of the enzyme for adenosine is 58 mM.
From the above result, it is suggested that the enzyme is different from ADase of soluble fraction of human placenta.
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