Human diploid lung fibroblast cell lines WI 26 and WI 38 exhibit isozyme shift of alkaline phosphatase after viral transformation.

The testing of the type of membrane associated alkaline phosphatase (EC 3.1.3.1) by immunotitration has revealed that there is a shift from a liver-like type of alkaline phosphatase in normal cell cultures of the human diploid fibroblast cell strains WI 26 and WI 38 to a placenta-like variant in cultures of the same cell strains after the transformation by the DNA-tumor virus SV 40, the WI 26 SV 40 and the WI 38 SV 40 cell lines. The immunologically detectable switch-over has been confirmed by measuring the apparent Michaelis constant and the heat stability of the AP from normal and transformed cells. Liver-like AP is heat labile and has an apparent Michaelis constant for p-nitrophenylphosphate (about 4.0 X 10(-4) M). The placenta-like AP shows heat stability and a lower apparent KM (about 2.2 X 10(-4) M). The appearance of the so-called Regan enzyme of AP in some human tumors in vivo is discussed in this connection.