Figure 2: Effect of Mg2+ on the activity of SeHAS single, double, and null Cys-mutants. A. HAS activity was determined in the presence of increasing concentrations of MgCl2, with no other divalent salts present, as described in Methods, using membranes containing wildtype or the indicated SeHAS double Cys-mutants. Panel B is a blow-up of the 0-1 mM range from A. The SeHAS variants are: wildtype, red circle; C(226,262)A, yellow triangle; C(226,281)A, green diamond; C(226,367)A, dark blue square; C(262,281)A, light blue inverted triangle; C(281,367)A, gray circle ; Cys-null, black square. C. Membranes containing single Cys-mutants were assayed as above: C(226)A, black triangle; C(262)A, black square; C(281)A, black circle; or C(367)A, black inverted triangle.