Studies on a variant alkaline phosphatase in sera of patients with hepatocellular carcinoma

Abstract

An alkaline phosphatase (orthophosphoric monoester phosphohydrolase, E.C. 3.1.3.1) was found in sera, ascitic fluid or cancer tissues of patients with hepatocellular carcinoma which had a different electrophoretic mobility from that of liver, bone, placental or intestinal isoenzyme. The enzyme was purified 300-fold from serum of one of these patients, and its enzymic properties were investigated. This variant alkaline phosphatase had almost identical properties to the placental isoenzyme with respect to inhibition by l -phenylalanine or l -homoarginine, inactivation by urea, susceptibility to the action of neuraminidase, molecular size, and antigenicity. The pH optimum and sensitivity to inhibition by phosphate were similar to those of the liver isoenzyme, but the enzyme was different from either one with respect to its susceptibility to l -leucine, Michaelis constant, electrophoretic mobility, and heat stability. The difference in enzymic properties among other variant alkaline phosphatases is also discussed.