Factors affecting the activities of Plasmodium falciparum GCH1. (A) Effect of temperature shift on the GCH1 activity as shown by the production of the oxidized neopterin product. (B) Effect of salt (KCl) on the GCH1 activity. (C) Effect of pH change on the activity of P. falciparum GCH1. The pH values were varied from pH 5–13 with the data point from pH 7.8, which was chosen for the enzymatic assay. Every reaction in Figure 3A-3C was performed for 90 minutes. (D) Effect of 8-oxo-GTP on the activity of P. falciparum GCH1. The inhibitory effect on initial velocity was followed under various substrate concentrations.