Hydrophobic properties of alkaline phosphatases

The butanol extraction method of Morton (1950), a routine step in enzyme purification, is discussed with special reference to a hydrophobic form of alkaline phosphatase from human liver tissue. This form slowly precipitates from butanol-extracted liver tissue homogenates stored at 4 degrees C. Furthermore, it is lost when acetone precipitation is applied as a purification procedure. The soluble form in liver tissue is shown to have a higher relative hydrophobicity than the serum liver/bone isoenzyme. The use of sodium cholate in the isolation of the hydrophobic form produces an artefact in isoelectric focusing, which can be abolished by dialysis prior to focusing.