FIGURE 6.

Effect of calcium metal ions on N-sulfamidase activity. A, calcium-specific requirement for N-sulfamidase activity and inhibition by EDTA wherein the divalent metal effect was not observed when calcium was replaced by either Mg²⁺ or Mn²⁺ (at either 1 or 5 mm concentrations). The following is the key: open bars (no divalent metals added); black bars (1 mm EDTA added); light gray bars (1 mm divalent metal); stippled gray bars (5 mm divalent metal). B, effect of calcium on steady-state kinetics of N-sulfamidase observed while varying concentrations of Ca²⁺ or in the presence of 1 mm EDTA. Substrate saturation plots were fitted to pseudo first-order Michaelis-Menten kinetics by nonlinear regression analyses. 0.5 mm Ca²⁺ (●), 1 mm Ca²⁺ (○), 5 mm Ca²⁺ (■). For clarification, the EDTA result (showing a lack of activity) is omitted.