Abnormal alkaline phosphatase of hepatic type in cerebrospinal fluid of a patient with intracranial metastasis from lung cancer.

High alkaline phosphatase (ALP) activity was found in the cerebrospinal fluid of a patient with intracranial metastases from adenocarcinoma of the lung. On agarose gel electrophoresis of the major ALP isoenzyme found in the cerebrospinal fluid, its mobility was different from those of the usual serum ALP isoenzymes. This abnormal mobility might be due to the linked glycan phosphatidylinositol anchor in the ALP molecule, as the mobility became the same as that of the common liver type ALP after treatment with phosphatidylinositol specific phospholipase. The immunochemical antigenicity of the cerebrospinal fluid ALP was identical with that of the common serum liver type ALP, but its sugar moiety was similar to the membranous liver-type ALP rather than the serum liver type ALP. The molecular size of the cerebrospinal fluid ALP was 140 kilodaltons, 12 less than the common serum liver type ALP, suggesting that the ALP in the patient's cerebrospinal fluid was derived from the intracranial metastatic carcinoma.