RNAse is an enzyme that cleaves the P-o5 bond in RNA. It has two His residues in
ID: 228733 • Letter: R
Question
RNAse is an enzyme that cleaves the P-o5 bond in RNA. It has two His residues in the active site. Suggest a plausible explanation why the enzyme activity changes when pH is increased or decreased from -pH 6.0 as shown in the graph below 120 100 80 E 60 40 Data provided by Dr. Sunita Chowrira 20 University of British Columbia 10 pH Choose all the true statements. The RNAse reaction is an example of metal ion catalysis with a positively charged metal The substrate is affected by the change in pH , and is inactive (+ charged) when pH is above ~6.0. Catalysis by RNAse is optimal when one His is protonated and the other is deprotonated. There are two His residues, and both are deprotonated below pH 4.2. Both His residues are deprotonated at pH higher than than 6.5Explanation / Answer
Solution:
In the catalysis by RNase, two histidines are considered as critical residues. There is a classic bell-shaped pH-rate profile for activity vs pH. Enzyme conformation is altered by pH change, which results in the change in activity. The true statement are:
Both His residues are deprotonated at pH higher than 6.5.
Catalysis by RNAse is optimal when one His is protonated and the other is deprotonated.
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