Effect Of pH on Enzyme Activity & Other Factors That Affect Catalytic Activity

Enzymes are essential to many biochemical processes in living organisms and industrial processes. But their action is highly sensitive to their environment. Temperature, pH, enzyme concentration, and the presence of inhibitors can have a positive or negative effect on enzyme activity.

In this article, the focus is on the effect of pH on enzyme activity. Little changes in pH can affect binding to substrates, the rate of catalysis by enzymes, and the conversion of substrates to products. These changes also affect the enzymes.

Continue reading to see the effect changes in pH have on enzyme activity and the optimum pH for different enzymes.

What is pH?

pH measures the concentration of H+ ions in a solution. The quantity of H+ ions in a solution measures the level of acidity or alkalinity of the solution.

This is measured using a pH scale that is numbered 0 to 10. Using this scale, solutions with pH values less than 7 are acidic, solutions with pH value 7 are neutral, and solutions with pH values greater than 7 are basic.

What is enzyme activity?

Enzyme activity is a property that measures the ability of an enzyme to increase the rate of reaction in a living organism. It measures how fast the substrate disappears or the rate at which the product is formed.

Enzyme activity is measured by micromoles of substrate used up or products formed per minute spent in the reaction.

How does pH affect enzyme activity?

When pH increases or decreases, enzyme activity decreases. The pH value at which enzyme activity is at its best is the optimum pH. Above or below this value, enzyme denaturation occurs. This is a process in which an enzyme loses its 3-D structure, biological activity, and catalytic properties.

An increase or decrease in pH disrupts the weak chemical bonds and interactions that determine the shape of the enzyme.  

Enzyme denaturation by pH can be reversible/temporary or irreversible/permanent. Under certain physiological conditions, if the optimum pH value is quickly restored, the enzyme may regain its structure and activity. In extreme cases, denaturation becomes permanent.

In the agricultural sector, maintaining optimum pH is necessary for soil health and crop productivity. pH values help to determine the texture, flavor, and shelf life of food in food industries.

The effect of pH on enzyme activity also has practical implications in drug development, diagnostic enzyme assays, bioremediation, the textile industry, wastewater treatment, and the production of detergent and cleaning products.

Additionally, some food industries also employ enzyme denaturation to tweak the textures and flavors of foods.

Enzymes and their optimum pH

Every enzyme has its optimum pH. Most enzymes are at their best between pH values 6 and 8. However, some work well under extremely acidic or basic conditions.

Some popular enzymes, their location, and optimum pH values are:

EnzymeLocationOptimum pH
PepsinStomach2.5
InvertaseSaliva4.5
MaltaseThe brush borders of the small intestine6.1 to 6.8
AmylaseSalivary gland and pancreas6.7 to 7.0
CatalaseLiver7.0
Protease Pancreas7.4 to 8.2
LipaseMouth, stomach, and pancreasMouth (4.5 to 5.4) Stomach (4.0 to 5.0) Pancreas (8.0)
TrypsinSmall intestine8.0 to 8.5
Alkaline phosphataseSmall intestine8.5 to 10.0

Other factors that affect enzyme activity

Other factors that affect enzyme activity are:

Temperature

As enzymes have their optimum pH, they also have their optimum temperatures at which they are more active.

At high temperatures, the reactants acquire more kinetic energy, and the transformation of substrates happens at a faster rate. When the temperature is lower, kinetic energy is lower as well and the rate of the reaction is slower.

Extremely high temperatures weaken and destroy the intramolecular bonds within the enzymes. This alters the shape and permanently denatures the enzyme.

On the other hand, low temperatures do not cause permanent denaturation. Once the temperature rises to the optimal value, enzyme activity will be restored.

Substrate concentration

Catalytic activity requires the binding of a substrate to the active site of the enzyme. The more substrates there are to bind, the higher the rate of catalysis and the faster the equilibrium shifts to the enzyme-product complex.

However, an oversaturation with substrates will not increase the rate of catalysis.

Enzyme concentration

The higher the concentration of enzymes, the higher the velocity of the reaction. When there are more enzyme molecules, there are more enzyme-substrate complexes, and the rate of catalysis becomes higher. Also, the reaction reaches equilibrium faster.

Presence of inhibitors and activators

Some enzymes require a metal ion or cofactor to initiate catalytic activity. Some need effectors – activators or inhibitors – to promote or inhibit binding to substrates.

When an inhibitor binds to the substrate or enzyme, it prevents catalytic activity. Inhibition can be irreversible or reversible. Irreversible inhibition happens when the inhibitor forms a strong bond with the enzyme and permanently inactivates it.

In reversible inhibition, the enzymes do not permanently inactivate the enzyme because they do not form permanent solid bonds. There are three types of reversible inhibition – competitive, noncompetitive, and uncompetitive.

An inhibitor with a similar geometry to the substrate is a competitive inhibitor. This inhibitor competes with the substrate for the active site of the enzyme. This type of inhibition is competitive inhibition, and it is usually temporary and reversible.

In noncompetitive inhibition, the inhibitor binds to another site on the enzyme and distorts the shape of the active site, thereby preventing the substrate from binding.

Uncompetitive inhibition is unique and different from the other types of reversible inhibition. The inhibitor binds to the enzyme-substrate complex and forms an enzyme-inhibitor-substrate complex that slows down catalytic activity.

This type of inhibition usually occurs in reactions where there is more than one substrate or product.

FAQs

Are there enzymes that are unaffected by pH?

No, there are no such enzymes. All enzymes are proteins, and their activity will be affected by lowered or very high pH.

Will enzymes adapt to pH changes over time?

No. Enzymes do not adapt to extremely high or low pH values. pH changes can either permanently damage the enzyme or the enzyme may return to its original state if the pH is quickly regulated.

Can pH be controlled?

Yes. Depending on the type of reaction, pH can be controlled using buffers. These buffers can be salts of a weak acid and a weak base.

Does pH change with temperature?

Yes, it does. pH drops as the temperature increases, and vice versa. However, this does not fully imply that a solution becomes more acidic at higher temperature values.

Conclusion

Enzymes seem to be independent biological molecules, but they depend on factors, such as pH, temperature, enzyme concentrations, and the presence of inhibitors. Enzymes generally function optimally within a narrow range of pH. This is their optimum pH.

When the pH changes, enzyme activity is no longer the same. It could become slower. In most cases, the enzyme loses its structure and becomes inactive. This explains the importance of enzymes in biological processes in medicine, biotechnology, and other industries.

Learn further with this comparison of hormones vs enzymes. Find out their similarities and differences.

Thanks for reading.