MARKED INCREASES IN DT DIAPHORASE ACTIVITY IN MALIGNANTLY TRANSFORMED SYRIAN-HAMSTER FIBROBLASTIC CELLS

NAD(P)H quinone oxidoreductase (DT diaphorase; EC 1.6.99.2) activity in cultured Syrian hamster fibroblastic cells was measured. The cells examined were classified into three categories: (1) four primary embryonic fibroblasts, (2) three non-malignant immortal cells and (3) four malignantly transformed cells. The results showed that cytosolic DT diaphorase activity in malignant cells was markedly higher than the corresponding activity in non-malignant cells (enzyme activity: (3) >> (1) greater-than-or-equal-to (2)). The enzyme activity was not influenced very much by the particular phase of cell growth. Thus, the increase in DT diaphorase activity seems to be a good marker for malignant transformation, at least in Syrian hamster fibroblastic cells.