Standardization of the alkaline phosphatase determination with human placental phosphatase

The influence of changes in temperature and salt concentrations on the enzymic activity of 3 different alkaline phosphatase preparations has been examined. Beef liver phosphatase is labile; the activity is already lost by lyophilization. Hog intestinal and especially human placental phosphatase are more stable. In contrast to reconstituted sera no preincubation is necessary to restore the enzymic activity. A lyophilized human placental phosphatase, kept at room temperature, showed no change in activity in a period of about one year. A mean value of enzymic activity of 133 U/l was observed with a coefficient of variation of 2.4% for 12 determinations. It is suggested to assign a value to such a preparation and to use it as a primary standard in the determination of the alkaline phosphatase.