Isolation and partial characterization of a 56,000-dalton phosphoprotein phosphatase from the blood-brain barrier

A 56,000-dalton protein with inherent phosphoprotein phosphatase activity was isolated from porcine brain capillaries. The enzyme is not activated by divalent metal ions but strongly inhibited by zinc ions. As phosphatase inhibitor 2 readily inhibits the enzymatic activity, the protein can be classified as a type I phosphatase. The protein is stable toward protease treatment. Limited digestion with trypsin does not convert the enzyme into an active form of lower molecular weight. The physical and enzymatical properties of the phosphatase exhibit considerable similarities to those of another 56,000-dalton phosphatase derived from rabbit reticulocytes.