1. FACTORS AFFECTING ENZYME ACTION
Enzymes are macromolecular biological catalysts. Enzymes accelerate, or catalyze, chemical
reactions. The molecules at the beginning of the process are called substrates and the enzyme
converts these into different molecules, called products. Almost all metabolic processes in the cell
need enzymes in order to occur at rates fast enough to sustain life.The set of enzymes made in a
cell determines which metabolic pathways occur in that cell. The study of enzymes is called
enzymology. There are various factors which affect the activity of enzymes. Some of them are as
under:
Substrate concentration
Enzyme concentration
Temperature
pH
Salt concentration
Substrate concentration
For a given amount of enzyme, an increase in substrate will result in an increase in the rate of
reaction. The more substrate molecules there are, the faster the reaction takes place as more of the
active sites are used. This continues until the concentration of substrate is so high that all the
enzyme molecules are working at their maximum capacity. At this point, however much more
substrate is added the reaction will not go any faster.
Graph showing effect of substrate concentration
on rate of Enzyme catalyzed reaction
2. Enzyme concentration
In order to study the effect of increasing the enzyme concentration upon the reaction rate, the
substrate must be present in an excess amount; i.e., the reaction must be independent of the
substrate concentration. Any change in the amount of product formed over a specified period of
time will be dependent upon the level of enzyme present.
The formation of product proceeds at a rate which is linear with time. The addition of more
substrate does not serve to increase the rate.
Graph to show the effect of enzyme concentration
On enzyme catalyzed reaction
Temperature
Like most chemical reactions, the rate of an enzyme catalyzed reaction increases as the temperature
is increased. A 10° C rise in the temperature will increase the activity of most enzymes by 50-
100%. Variation in the reaction temperature, as small as 1 -2° C, may introduce a 10-20% increase
in the reaction rate.Most enzymes are adversely affected by a temperature above 40° C.
3. Enzymes lose their activity at extremely low temperatures as well. This may account for storing
enzymes at 5° C or below without affecting enzymatic activity permanently.
pH
The pH of the environment has a major effect on the rate of enzyme controlled reactions. The
intermolecular bonds – particularly the hydrogen bonds – that maintain the tertiary structure and
the active site are very vulnerable to changes in hydrogen ion concentration. Each enzyme has an
optimum pH at which it works at its optimum rate. A change in pH causes a change in the shape
of the active site. It is not so easy for the reactants to fit in and bind to the active site. The activity
of the enzyme is reduced and the rate of reaction slows. If the change is too great, the substrate
will not be able to bind to the active site at all and the enzyme can no longer catalyse the reaction.
In most cases the activity of the enzyme is restored as the pH returns to its optimum level.
Graph to show effect of pH on enzyme catalyzed
Reaction
Salt concentration
Some enzyme need less salt,bits of NaCl can incresase its activity.But high amount of NaCl affect
the strcture of pritein,then influlence activity. Not just the concentration of salt, but also the identity
of the ions, and the ionic strength of the solution can affect the activity of an enzyme. It is worth
taking the time to try out various salts at a range of concentrations to find the optimal conditions
for an enzyme.
4. Inhibitors of enzyme action
An enzyme inhibitor is a molecule that binds to an enzyme and decreases its activity. Since
blocking an enzyme's activity can kill a pathogen or correct a metabolic imbalance, many drugs
are enzyme inhibitors. They are also used in pesticides. Not all molecules that bind to enzymes are
inhibitors; enzyme activators bind to enzymes and increase their enzymatic activity, while enzyme
substrates bind and are converted to products in the normal catalytic cycle of the enzyme
Reversible inhibitors
Reversible inhibitors attach to enzymes with non-covalent interactions such as hydrogen bonds,
hydrophobic interactions and ionic bonds. Multiple weak bonds between the inhibitor and the
active site combine to produce strong and specific binding. In contrast to substrates and irreversible
inhibitors, reversible inhibitors generally do not undergo chemical reactions when bound to the
enzyme and can be easily removed by dilution or dialysis. They may be competitive or non
competitive.
In competitive inhibition, the substrate and inhibitor cannot bind to the enzyme at the
same time, as shown in the figure on the right. This usually results from the inhibitor having
an affinity for the active site of an enzyme where the substrate also binds; the substrate and
inhibitor compete for access to the enzyme's active site.
In non-competitive inhibition, the binding of the inhibitor to the enzyme reduces its
activity but does not affect the binding of substrate. As a result, the extent of inhibition
depends only on the concentration of the inhibitor. Vmax will decrease due to the inability
for the reaction to proceed as efficiently, but Km will remain the same as the actual binding
of the substrate, by definition, will still function properly.
