In the presence of effector A an enzyme displays sigmoidal behavior when initial velocity is plotted against substrate concentration. With increasing concentrations of A the curve is displaced to the left (i.e., towards the ordinate). Effector A is thus
A) a positive allosteric effector.
B) a competitive inhibitor.
C) a negative allosteric effector.
D) a non-competitive inhibitor.
E) an uncompetitive inhibitor.

Question

Quizplus · Accepted Answer

The sigmoidal behavior indicates cooperative binding of the substrate to the enzyme. The displacement of the curve to the left indicates an increase in affinity of the enzyme for the substrate. This kind of behavior is seen in positive allosteric effectors, which bind to the enzyme and enhance substrate binding.

In the Presence of Effector a an Enzyme Displays Sigmoidal