Plasma membranes have been prepared from rat normal liver cells, regenerating liver cells and Yoshida
ascites hepatoma 66 cells after intact cells were first bound to
polylysine-coated
polyacrylamide beads, and the membrane-associated
Mg2+ -ATPase activity was assayed directly on beads with membrane attached. With plasma membranes from normal liver cells, Km for
ATP and V were found to be higher than those in regenerating liver cells and
hepatoma cells.
Vanadate caused a different sensitivity of the activity, without an effect in normal liver cells and with an inhibition in regenerating liver cells and
hepatoma cells. The activity in normal and regenerating liver cells decreased with increasing temperature above 24-30 degrees C, while the activity in
hepatoma cells continued to increase linearly to 37 degrees C. Unlike the
enzyme in normal and regenerating liver cells, the
hepatoma enzyme was shown to have a higher phase transition temperature and lower activation energies. In all three kinds of cells the activity was increased by the dephosphorylation of plasma membranes and unaffected by the phosphorylation. By means of histochemical
Mg2+ -ATPase staining applied on
polyacrylamide gels, at least three major bands which show the enzymic activity were visible in normal and regenerating liver and a single band was detected in
hepatoma cells.