Figure 5: The activities of SeHAS wildtype, double and null Cys-mutants are differentially affected by Ca2+ , Ni2+ or Cu2+ . Membranes containing SeHAS wildtype, null, or double Cys-mutants (coded as noted in the Panel A insert) were incubated in the presence of 20 mM MgCl2 and the indicated concentrations of either CaCl2 (A) or CuCl2 (B) and HA synthase activity was determined as described in Methods. The SeHAS variants in A and B are: wildtype, red circle; Cys-null, black square, C(226,262)A, green triangle; C(226,281)A, blue diamond; C(226,367)A, yellow hexagon; C(262,281)A, light blue inverted triangle; C(281,367)A, gray circle. C. Membranes containing wildtype (○, □) or Cys-null (●, ■) SeHAS were incubated in the presence of 20 mM MgCl2 and the indicated concentrations of CuCl2 (●, ○) or NiCl2 (■, □) and HA synthase activity was determined as described in Methods.