CALMODULIN-DEPENDENCY OF A CA2+-PUMP AT THE PLASMA-MEMBRANE OF CULTURED CARROT CELLS

Activity of a Ca2+-translocating ATPase which functions as a Ca2+-pump was found to be associated with a highly purified plasma membrane fraction of cultured carrot cells. Different classes of calmodulin antagonists trifluoperazine and W-7 - appreciably inhibited ATP-driven uptake of Ca2+ into the sealed vesicles of the membrane. The incorporation of Ca2+ was also markedly inhibited in the presence of anti-calmodulin IgG. This translocating activity was significantly decreased when the vesicles were washed with EGTA-containing buffer; however, it was restored to almost the control level upon the addition of exogenous calmodulin. These results suggest that the Ca2+-pumping ATPase at the plasma membrane of cultured carrot cells is regulated by calmodulin, and the modulator protein associates with the enzyme in a Ca2+-dependent manner.