An enzymeʹs active site contains an arginine residue and a glutamate residue with pK_aʹs of 2.9 and 9.1, respectively. Both residues are actively involved in the catalytic mechanism and they are the only two ionizable residues in the active site. What would you expect for the optimum pH of the enzyme? A) 6.0 B) 7.0 C) 7.4 D) No pH can be determined since the information is irrelevant to the optimum pH.

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Quizplus · Accepted Answer

The optimum pH is typically between the pKa values of the ionizable residues involved in catalysis. Here, it would be between 2.9 and 9.1, so around 6.0.

An Enzymeʹs Active Site Contains an Arginine Residue and a Glutamate