Human Placental Alkaline Phosphatase: Expression inPichia pastoris,Purification and Characterization of the Enzyme

The soluble form of human placental alkaline phosphatase (PLAP) was expressed in the methylotrophic yeastPichia pastorisand the expression product was purified and characterized. Yeast-derived PLAP (yPLAP) was secreted into the medium to the level of 2 mg/liter. yPLAP displayed kinetic properties similar to those reported earlier for the membrane-bound PLAP. Purified yPLAP had specific activity of 774 U/mg and appeared in two subunit sizes, ca. 62 and 65 kDa. This difference was due to heterogenous N-glycosylation. Purified yPLAP appeared as multiple forms in isoelectric focusing in pIrange of 4.2 to 5.2. The expression system is discussed in comparison to previously reported expression systems.