The isolation, purification and some properties of the alkaline phosphatase of human leucocytes

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Abstract
The isolation and partial purification of the alkaline phosphatase of normal human leucocytes was described. A 250-fold purification was attained with the best preparation, having a specific activity of 4075 [mu]g of P/ mg of N/hr. The purified enzyme contained 44.1 [mu]g. of Zn/mg of N. The less-purified preparation was capable of liberating inorganic P from a wide variety of substrates, including mono-, di- and triphos-phorylated nucleotides. The monophosphorylated nucleotides were apparently most susceptible to enzyme attack. Of the sugar intermediates, the C5 chain with P substituted on the end carbon atom appeared to be most labile. The purified enzyme exhibited first-order kinetics with the substrates tested and competitive data suggest that the liberation of inorganic P may be due to a single enzyme rather than to a multiple enzyme system, provided that no inhibition occurs. No specific physiological role can as yet be ascribed to the leucocyte alkaline phosphatase.