Formation of an alkaline phosphatase-immunoglobulin G complex in human sera.

An electrophoretically slow-moving band of alkaline phosphatase (ALP) isoenzyme was found in four patients with chronic liver disease and in one with ulcerative colitis. Immunoelectrophoretic studies revealed that the slow band was a complex containing alkaline phosphatase and an immunoglobulin G of the lambda class. Its molecular weight was approximately 280 000. A complex molecule consisting of one molecule of immunoglobulin G and one molecule of alkaline phosphatase was proposed. The complex was similar to the liver and bone alkaline phosphatases in functional properties. Serum containing the complex was capable of binding liver and bone alkaline phosphatase isoenzymes but not the intestine or placenta alkaline phosphatase isoenzymes from normal controls. The presence of an abnormal immunoglobulin which binds liver and bone alkaline phosphatases appears to be responsible for the development of the complex. In one case of chronic liver disease, the complex disappeared after a few months.