Properties of Amphiphilic and Hydrophilic Forms of Alkaline Phosphatase from Human Liver

Abstract

Amphiphilic and hydrophilic forms of alkaline phosphatase differed in electrophoretic mobility, sensitivity to heat, activation by phospholipids and albumin, and affinity of monoclonal antibodies, but were similar in substrate K(m) and inhibitor K(1) values, sensitivity to sodium dodecyl sulfate, and electrophoretic behavior on desialylation. Chemical cross-linking experiments failed to conclusively demonstrate an aggregated state of amphiphilic alkaline phosphatase in Triton X-100. Further, attempts to identify a polymeric hybrid between amphiphilic forms of human liver and placental alkaline phosphatase were unsuccessful. We conclude that the covalent attachment of the hydrophobic phosphatidylinositol membrane anchor causes the amphiphilic form to behave anomalously on electrophoresis and to affect certain of the enzyme’s catalytic and physical properties.