Problem: RNase is an enzyme that cleaves the P-O5' bond in RNA. It has two His residues in the active site. Which of the following statement(s) could explain why the enzyme activity changes when pH is increased or decreased from pH 6.0 as shown in the graph? Choose one or all that apply. RNase is an enzyme that cleaves the P-O5' bond in RNA. It has two His residues in the active site. Which of the following statement(s) could explain why the enzyme activity changes when pH is increased or decreased from pH 6.0 as shown in the graph? Choose one or all that apply. Both His residues are deprotonated at pH higher than 6.5. There are two His residues and both are deprotonated below pH 4.2. The substrate is affected by the change in pH and is inactive (positively-charged) when pH is above 6.0. Catalysis by RNase is optimal when one His is protonated and the other is deprotonated.