Comparison of a tumour-derived form of intestinal alkaline phosphatase with foetal and adult intestinal alkaline phosphatases.

An intestinal alkaline phosphatase-like (Kasahara) isoenzyme has been isolated from the serum of a patient with lung cancer and compared with foetal intestinal alkaline phosphatase from the serum of a premature infant and with adult intestinal phosphatase isolated from serum in the same way. Although the ligand-binding sites of the three enzymes were indistinguishable, the foetal intestinal and Kasahara isoenzymes differed slightly from the adult isoenzyme in heat stability and markedly in electrophoretic mobility and neuraminidase-sensitivity, while themselves being similar in these respects. Neither the Kasahara isoenzyme nor foetal phosphatase reacted with anti-placental phosphatase monoclonal antibodies. These results suggest that the Kasahara isoenzyme corresponds to the reappearance of foetal intestinal alkaline phosphatase, rather than to modification of the adult intestinal isoenzyme.