Human Alkaline Phosphatases. I. Purification and Some Structural Properties of the Enzyme from Human Liver

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Abstract
Alkaline phosphatase (EC 3.1.3.1) from human liver was purified to homogeneity. It is a glycoprotein of MW .apprx. 136,000. Analysis of the subunit structure by sedimentation equilibrium in 6 M urea and by dodecylsulfate polyacrylamide gel electrophoresis of the denatured enzyme indicated MW of .apprx. 35,000 and 32,000, respectively. The human liver alkaline phosphatase seems to be a tetramer composed of identical or very similar subunits. The purified enzyme has a specific activity of 1360 .mu.mol/(min .times. mg protein), corresponding to a molecular activity of 3170 s-1. The enzyme retains full activity in 1% sodium dodecylsulfate for several hours. The isoelectric point of the native enzyme is 4.2. After treatment with neuraminidase the isoelectric point increases to 6.5.