Factors Affecting Enzyme Activity: pH, Substrates

Definition Of Enzymes

They are protein molecules that act as catalysts and enhance the rate of chemical reactions by lowering the activation energy required for any reaction to proceed. In other ways, they do it in a very specific manner, recognising specific substrates, and then, through precise mechanisms or pathways, converting the substrates into products.

Importance Of Enzymes In Biological Processes

Almost all biochemical processes that are important for life depend on enzymes. Some examples of these processes are digestion, metabolism, DNA replication and cellular respiration. Without enzymes, these reactions would proceed too slowly for life to exist.

It is because of their unique three-dimensional shapes that enzymes obtain specificity. These unique shapes permit specific substrates to bind at the active site of an enzyme where they are converted into products. In this way, there is limited binding of the wrong substrate, which would decrease the integrity of the biological process by generating the wrong product.

Enzyme Activity Regulation And Factors Affecting It

The activity of enzymes is tightly regulated to provide homeostasis in cells and also to adjust to environmental changes. This may be through temperature, pH, concentration of substrate, inhibitors of enzymes, and also cofactors and coenzymes. Having a feel for some of these regulatory mechanisms helps particularly in knowing how an optimum enzyme could function under varying biological conditions.

Temperature And Enzyme Activity

• Temperature, in general, increases enzyme activity since there is heightened motion of molecules that results in increased collision.

• There exists an optimum temperature for each enzyme, where its activity is maximum. For example, most human enzymes have optimum temperatures near 37°C.

• High temperatures can disrupt the enzyme structure, changing in this way the shape of its active site, which is more important for substrate binding.

• Extreme temperatures can denature enzymes, and the molecule cannot function.

• Examples: Enzymes in brewing and baking are temperature-sensitive.

• Industrial processes like pharmaceutical production are done in controlled enzyme temperatures for efficiency.

pH and Enzyme Activity

• Each enzyme has an optimal pH at which the rate of the reaction is highest.

• At this pH value, these enzymes have their normal configurations.

• A change in pH can alter the ionization of the side chains and disrupt normal interactions. Under extreme conditions, pH, in fact, inactivates the enzyme.

• Examples: Digestive enzymes- amylase in the mouth has an optimum pH of about 7. Pepsin in the stomach has an optimum pH of about 2.

Substrate Concentration And Enzyme Activity

• Generally, enzyme activity increases with an increase in substrate concentration because more and more substrate molecules collide with the enzyme.

• That is, more products are generated per unit of time as more substrate molecules occupy active sites.

• But when the active sites are filled almost continuously with substrate, the rate of the reaction cannot increase any more. The maximum rate has been reached.

• Michaelis Menten Constant, Km explains the concentration of substrate required to produce a reaction that is equal to half of the maximum velocity of the reaction.

• For example, the Km decreases when the competitive inhibitor is included.

Enzyme Inhibitors

Enzyme inhibitors are of three types:

Competitive Inhibition

• It occurs because the molecule of the inhibitor binds to the active site of the enzyme.

• An inhibitor molecule is similar enough to the substrate.

• This is known as competitive inhibition because, in effect, an inhibitor is competing with the substrate for the active binding site.

• An example of a use for a competitive inhibitor is in the treatment of influenza via the neuraminidase inhibitor, Relenza.

Uncompetitive Inhibition

• Sometimes, binding of the substrate to the active site changes the conformation of the enzyme.

• It creates an allosteric site that was not present earlier, before the binding of the substrate.

• This is the site to which an inhibitor binds and exerts its inhibitory effect.

• It cannot be overcome by increasing substrate concentration.

Non-Competitive Inhibition

• Some enzymes have permanent allosteric sites that can bind to the inhibitor.

• As the inhibitor does not compete for the active site, it is called non-competitive inhibition.

• It is also called allosteric inhibition.

• In non-competitive inhibition, the Km does not change.

• This is because Km is a measure of the affinity of the enzyme for its substrate and this can only be measured by the active enzyme.

• The fixed amount of inactive enzyme in non-competitive inhibition does not affect the Km and, therefore, is unchanged.

• An example of a use for a noncompetitive inhibitor is in the use of cyanide as a poison (prevents aerobic respiration)

Cofactors And Coenzymes

• Many enzymes require their functionality to be assisted by cofactors and coenzymes, two general terms for molecules that facilitate biochemical reactions.

• Cofactors can be either inorganic, that is, a metal ion, or organic molecules, but they are not proteins.

• Some examples of cofactors are the zinc ion Zn²⁺ in carbonic anhydrase and the magnesium ion Mg²⁺ in hexokinase.

• Coenzymes are organic molecular helpers, especially vitamin derivatives.

• They can work along with an enzyme to serve in a reaction, but still, they can work independently in the cell.

• Examples of coenzymes include NAD⁺, FAD, and Coenzyme A. Enzymes can best conduct catalytic activities using such molecules, therefore allowing the transfer of chemical groups during a reaction.

Enzyme Activity Regulation

• Molecules can bind to allosteric sites on enzymes, inducing a conformational change that either increases or decreases enzyme activity.

• Such regulation allows for fine control of metabolic pathways in response to cellular demands.

• One of the end products in a metabolic pathway can inhibit enzymes in earlier steps in the pathway to prevent too much of the end product from being made.

• The cell is self-regulating and efficiently uses its resources through these types of mechanisms.

• Enzyme induction is the process whereby the synthesis of that enzyme is increased by a substrate or environmental change.

• Enzyme repression: when the product is in excess or when there is a high abundance of a repressor molecule, enzyme synthesis is repressed, thus conserving energy and resources.

• Enzyme cascades: several metabolic pathways in cells are mediated by cascades of enzymatic reactions that could potentially amplify signals greatly.

• Allosteric regulation in glycolysis: In this, ATP is an allosteric inhibitor of phosphofructokinase. Whenever energy levels in the cell are high, ATP binds to phosphofructokinase and inhibits it, and that is a turn off this pathway.

Conclusion

The factors affecting enzyme activity are temperature, pH, substrate concentration, presence of inhibitors, cofactors, and coenzymes. Under these circumstances, these factors are important to know in order to understand how an enzyme functions. Moreover, enzyme kinetics has key implications for both biological and industrial applications.

In the context of a biological system, it aids in regulating metabolic processes. This occurs so that the entire process becomes efficient and properly balanced. In industrial applications, on the other hand, the engineering and optimisation of enzymes have huge potential for increasing productivity and sustainability. However, future research in enzyme technology has more in store for the biocatalysis phenomenon, so that biocatalysis could better benefit healthcare, environmental management, and several industrial processes.