AN UNUSUAL HIGH-K-M HEXOKINASE IS EXPRESSED IN THE MHAT3F HEPATOMA-CELL LINE

In most hepatoma cells, the high-K-m GLUT2/glucokinase proteins are re placed by the ubiquitous low-K-m GLUT1/hexokinase type I proteins. In the mhAT3F hepatoma cells, the stimulatory effect of glucose on gene e xpression and glycogen accumulation was not maximal at 5 mmol/liter gl ucose. This response to high glucose is observed in mhAT3F cells, wher e GLUT2 was expressed, but not glucokinase (assessed by Northern blott ing and reverse transcription-polymerase chain reaction). A low-K-m he xokinase activity (19.6 +/- 3.8 milliunits/mg of protein) was present, but a high-K-m (40 mmol/liter) hexokinase activity (13.9 +/- 2.5 mill iunits/mg) was also detected in mhAT3F cells. The high-K-m hexokinase activity was dependent on both ATP (or PP,) and glucose in the assay a nd was recovered in a 10-50-kDa fraction after filtration. A 30-kDa pr otein was detected using an anti-glucokinase antibody and localized by confocal microscopy at the same sites as glucokinase in hepatocytes. In FAO cells, the high-K-m hexokinase activity and 30-kDa protein were not found. We conclude that a high-K-m hexokinase activity is present in mhAT3F cells. This might explain why the effects of glucose on gen e expression were not maximal at a glucose concentration of 5 mmol/lit er. A 30-kDa protein identified using an antiglucokinase antibody may be responsible for this activity present in mhAT3F cells.