Murine lymphoma alkaline phosphatase: a cell membrane carcinofetal enzyme

Alkaline phosphatase (APase) has been shown to have a membrane-bound localization in the murine fetal thymus, in murine thymic lymphoma and in adult spleen. Since it was suggested from these previous experiments that the lymphoma APase might represent an embryonic function, a detailed biochemical comparison of the lymphoma APase with the fetal thymus, placenta, fetus and spleen APases was performed. The parameters investigated were pH optimum, activation, inhibition, heat inactivation, substrate ratios, Michaelis constant, and electrophoretic analysis in the presence and absence of neuraminidase with the substrates alpha-naphthyl phosphate, beta-glycerophosphate, and p-nitrophenyl phosphate. The results indicate that the lymphoma APase is very similar to the fetal thymus, placenta and spleen APases. Furthermore, these results lend support to the hypothesis that the APase activity which appears in thymic lymphoma might represent a derepressed embryonic function. Thus, the murine lymphoma APase may be termed a cell membrane carcinofetal enzyme.