Alkaline phosphatase (AP) has been characterized in the neutrophil polymorphonuclear
leukocytes (PMN) from 14 healthy adults. The biochemical properties of the isoenzymes
were analyzed by the following methods: enzyme assays, slab gel electrophoresis, thermostability,
inhibition pattern using four chemical inhibitors, and immunological specificity.
In normal PMNs, two types of AP have been found: a thermolabile isoenzyme identical to the
liver/bone/kidney type and a thermostable isoenzyme with respect to its electrophoretic properties,
its level of thermostability, its immunological specificity, the thermostable isoenzyme
resembles the placental form more closely than the intestinal form. These results are consistent
with the proposal that granulocyte AP is a heterogeneous enzyme. Two enzyme forms
appear to be expressed in this blood cell.