FIGURE 2.

XLG2 has GTPase activity in the presence of Ca²⁺. A, GTPase activity of GPA1 and XLG2C in the presence of different divalent cofactors. GTPase activity was measured using the PEI-cellulose TLC plate method. B, GTPase activity of XLG2 and lack of GTPase activity of XLG2C(T475N) in the presence of CaCl₂. The reactions were performed as described in A. Aliquots (2 μl) were withdrawn after incubation for 2 h and then separated by TLC. C, substrate competition test for XLG2 in the presence of CaCl₂. Reactions were performed as described in A in the presence of competitors (3 μm unlabeled GTPγS, GDP, or ATP). The graph was drawn using quantitative TLC results (supplemental Fig. 2A) measured by ImageJ software. GTP hydrolysis was calculated as GDP/(GTP + GDP). GTP hydrolysis in the absence of competitor was designated as 100%. Error bars, S.D.