Figure 4. Calcium dependency of heat sensitivity of LUPOs from Lepidium. Peroxidases from Lepidium dissolved in buffers of different [Ca²⁺]_free as indicated on the X-axis were treated with a range of different temperatures (as in Figure 3). The remaining activity after heat treatment was measured and the ET₅₀ was evaluated for each calcium concentration. Here, ET₅₀ is plotted against the corresponding [Ca²⁺]_free and a curve was fitted to the data by sigmoidal curve fitting.