A pH versus rate curve with an inflection point at pH~4 suggests the involvement of a(n)________ in the catalytic step.
A)proton abstraction that requires a metal ion in close proximity
B)proton transfer with a pK close to 4
C)proton donation that is mediated by a coenzyme
D)free proton surrounded by a hydrophobic environment
E)redox cofactor

Question

Quizplus · Accepted Answer

An inflection point on a pH versus rate curve indicates a change in the ionization state of a functional group involved in the reaction. In this case, the inflection point is at pH~4, suggesting the involvement of a proton transfer with a pK close to 4. This is consistent with many enzymatic reactions that involve acidic or basic residues whose ionization state changes with pH.

A PH Versus Rate Curve with an Inflection Point at PH~4