RNAse is an enzyme that cleaves the P-O^5 bond in RNA. ft has two His residues i
ID: 490229 • Letter: R
Question
RNAse is an enzyme that cleaves the P-O^5 bond in RNA. ft has two His residues in the active 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. Choose all the true statements. There are two His residues, and both are deprotonated below pH 4.2. The RNAse reaction is an example of metal ion catalysis with a positively charged metal. Both His residues are deprotonated at pH higher than 6.5. 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.Explanation / Answer
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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