Enzymes are proteins produced by living cells. Enzymes are biochemical catalysts that
lower the activation energy needed for a biochemical reaction to occur. Because of enzyme
activity, cells can carry out complex chemical activities (Illanes, 2008, pp. 1-4). The substrate is
the substance acted upon in an enzyme-catalyzed reaction, and the substrate can bind reversibly
to the active site of the enzyme. The active site is the portion of the enzyme that interacts with
the substrate so that any substrate that blocks or changes the shape of the active site affects the
activity of the enzyme (Likhtenshtein, 2002, pp. 139). The result of this temporary union is
called the enzyme-substrate complex and reduces the amount of energy required to activate the
reaction of the substrate molecule so that products are formed (Illanes, 2008, pp. 8).
Inhibitors interact with an enzyme so that the activity of an enzyme is altered. An
inhibitor decreases or stops the activity. Inhibitors regulate how fast an enzyme acts. Inhibitors
work by unfolding or destabilizing bonds, thus denaturing the enzyme. Some inhibitors block or
change the shape of the active site (Schulz, 1994, p. 30).
In competitive inhibition, the substrate and inhibitor have both the same shape and
cannot bind to the enzyme at the same time, which usually results in the substrate and inhibitor
competing for access to the enzyme's active site (Schulz, 1994, p. 35).
If the competitive
inhibitor reaches the enzymes first, the reaction that is usually caused by the enzyme never
occurs (Schulz, 1994, p. 35). Competitive inhibition can be type of inhibition can be overcome
by sufficiently high concentrations of substrate; essentially the substrates out compete the
inhibitor (Schulz, 1994, p. 35). In non-competitive inhibition, the inhibitor reversibly binds to an
allosteric site, a site different than the active site, on the enzyme, preventing the substrate from
being able to bind to the active site and the reaction of the enzyme (Illanes, 2008, pp. 116).