[Cow's milk alkaline phospharase. II. Subunit structure, metalloproteic nature and kinetic parameters (author's...

Alkaline phosphatase (EC 3.1.3.1) from cow's milk as a dimer comprising two identical or very similar subunits of about 85 000 molecular weight. The enzyme contains 4.9 +/- 0.6 gatoms of zinc per mol of protein. The essential kinetic properties are the same as those of other alkaline phosphatases: variation of pH optimum value, the lack of specificity, increase of Km and V with pH value. The phosphotransferase activity is enlarged, at constant concentration of acceptor, with an increasing concentration of donor. The small size of molecules and the presence of hydroxyls and amino groups increase the percentage of transfer phosphate. The phosphotransferase reaction is better with the D-isomer of serine and the enzyme possesses a more important affinity for the D-phosphoserine.