Fig. 3. Ca²⁺ and Mg²⁺-ATPase activities in Drosophila melanogaster microsomal membrane fractions: thapsigargin sensitivity. Experiments were done with 1 µg of microsomal protein as outlined in Materials and Methods. Panel A indicates the activities of Mg²⁺ (filled) and Ca²⁺-ATPases (crosshatched). Different ATPases activities were obtained in the WT and YW stocks used. The results are expressed as mean±s.e.m. of five independent experimental observations. Panel B shows the inhibition of the Ca²⁺-ATPase activity promoted by increasing concentrations of thapsigargin. The results are the mean of 5 independent experimental observations. Standard errors are not shown, but in all cases were smaller to 15% of the mean value. The IC₅₀ obtained for thapsigargin was 80 µM.