Enzyme specificity depends upon its surface geometry. An enzyme has a specific portion of its three-dimensional structure called the active site. A substrate binds to this particular site. However, in some instances, an enzyme undergoes conformational changes in the process of bonding to improve the enzyme-substrate fit. This is referred to as induced-fit.
Some enzymes require the presence of a cofactor, some of which are called coenzymes.
There are several mechanisms for enzyme control. Another control device is a noncompetitve inhibition called allosteric inibion. In this case, an enzyme exists in two different forms - one active and one inactive. Negative modulators act to stabilize the enzyme in its inactive form which prevents it from interacting with its substrate.