NBME 21

nbme21/Block 3/Question#37

A 5-year-old boy who has homocystinuria improves ...

The line on the graph labeled ‘B’

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submitted by navevan3(0),

For this question, I was thinking that they asked you compare to a “normal” person, so the Vmax wouldn’t change since they state that his activity returns to a normal level. Only the x-axis would since it would be at increased concentrations in comparison.


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submitted by stapes2big(0),

The question is basically setting up a situation similar to that of a competitive inhibitor. They say that higher concentrations of pyridoxal phosphate increases the activity of the enzyme to normal levels. Similarly, when you have a competitive inhibitor and increase the concentration of substrate, the enzyme can achieve the same Vmax as if without the inhibitor.