The induced-fit theory

The key–lock hypothesis does not fully account for enzymatic action; i.e., certain properties of enzymes cannot be accounted for by the simple relationship between enzyme and substrate proposed by the key–lock hypothesis. A theory called the induced-fit theory retains the key–lock idea of a fit of the substrate at the active site but postulates in addition that the substrate must do more than simply fit into the already preformed shape of an active site. Rather, the theory states, the binding of the substrate to the enzyme must cause a change in the shape of the enzyme that results in the proper alignment of the catalytic groups on its surface. This concept has been likened to the fit of a hand in a glove, the hand (substrate) inducing a change in the shape of the glove (enzyme). Although some enzymes appear to function according to the older key–lock hypothesis, most apparently function according to the induced-fit theory.

Portion of the Encyclopædia Britannica Article