Figure 4: Mg2+-dependence of purified SeHAS and the effects of other divalent cations on enzyme activity. A. Purified SeHAS was incubated with the indicated concentration of MgCl2 in the absence of any other divalent metal ions (dashed line, black circles). In separate experiments, purified SeHAS in the presence of 20 mM MgCl2 was incubated with the indicated concentrations of one of the eight divalent cation chloride salts noted in the symbol legend (right of figure), and HA synthase activity was quantified as described in Methods. The divalent cations salts tested were: MnCl2 (black triangle); CuCl2 (blue inverted triangle); CoCl2 (green hexagon); CaCl2 (white circle); BaCl2 (white square); NiCl2 (white triangle); ZnCl2 (yellow hexagon); SrCl2 (black square). B. Purified SeHAS (○) and SpHAS (●) were assayed in the presence of 20 mM MgCl2 and the indicated concentration of CuCl2.