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Enzyme Activity: Overview & Effect on pH

Ranaa Aboumosallam Arafat, Sarah Phenix
  • Author
    Ranaa Aboumosallam Arafat

    I took pre-masters and diploma in Microbiology, Human Physiology and Endocrinology. I got accepted to start my masters next fall at the University of Manitoba in Biology. I wrote lessons for Michigan virutal and I worked as a biology teacher for one year. Moreover, I wrote scientific explainers and presentations for several educational platforms.

  • Instructor
    Sarah Phenix
Learn about the effect of pH on enzyme activity. Understand the interaction between enzymes and pH, the effect of pH on enzyme activity, and how pH affects it. Updated: 06/08/2022

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What are Enzymes?

On average, food takes several hours to a few days to be completely digested and absorbed in the body. This is because the presence of enzymes speeds up the rate of the digestion process. Without enzymes, food would take ages to be digested and absorbed. Enzymes serve as catalysts that speed up the rate of creation without affecting the reaction itself. Enzymes function by lowering the activation energy needed for the reaction to take place. Activation energy is the minimum amount of energy required for the reaction to occur. This means that it reduces the energy cost and increases the rate of a chemical reaction. In fact, without enzymes, the human body would not function properly because the chemical processes essential to maintain the body would simply not occur quickly enough. The nature of enzymes is protein-based; all enzymes are proteins but not all proteins are enzymes. Proteins are made up of several amino acids linked together by peptide bonds forming polypeptide chains. The enzyme itself is not affected or consumed during the reaction, however, it remains as it is and is able to catalyze other reactions.

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  • 0:03 What Are Enzymes?
  • 1:42 What Is pH?
  • 3:12 PH and Enzymes Interaction
  • 4:08 Optimal pH
  • 5:17 Inactive Enzymes
  • 5:59 Lesson Summary
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What is pH?

The "p" in pH stands for potenz, which signifies power in German, while the "H" stands for hydrogen. The pH is simply defined as the measurement of the concentration of hydrogen ions. The pH is an indication of the acidity, alkalinity, and neutrality of a liquid or aqueous solution. The range of pH starts from 0 and ends at 14. pH measurements depend on the concentration of hydrogen (H+) and hydroxide ions (OH-). When the hydrogen ion in a solution exceeds the concentration of hydroxide ions, the solution is said to be acidic. When the hydroxide ion in a solution exceeds the concentration of hydrogen ions, the solution is said to be basic.

  • When pH measures from 0 to less than 7, it indicates an acidic solution because the concentration of hydrogen ions is larger than that of hydroxide ions. 1 is the strongest acid, while 6.9 is the weakest acid. Hydrochloric acid is an example of a strong acid. Water is an example of a neutral liquid.
  • When pH measures 7, it indicates a neutral solution because the concentration of hydrogen ions is equal to the concentration of hydroxide ions.
  • When pH measures from more than 7 to 14, it indicates an alkaline or basic solution because the concentration of hydroxide ions is larger than that of hydrogen ions. 7.1 is the weakest alkaline, while 14 is the strongest alkaline. Sodium hydroxide is an example of a strong base.


pH scale and some examples of acidic and basic substances

pH scale and some examples of acidic and basic substances


Effect of pH on Enzyme Activity

Enzyme activity is defined as the rate of the reaction catalyzed by an enzyme and is represented as the conversion of substrate to product per minute. The activity of enzymes is affected by many factors which include pH and temperature. So, enzymes and pH are correlated. So, why does pH affect enzyme activity? pH affects enzyme activity because enzymes are proteins that get their molecular structure via interactions between the charges of the amino acids that form the protein chains. These interactions are in the form of a hydrogen bond which is affected by the pH level. How does pH affect enzyme reaction rate? Each enzyme has an optimal pH value. The optimal pH of an enzyme is the ideal pH value that the enzyme works the best in, or in other words, the value of the pH where the enzymatic activity is the highest. When the pH decreases below the optimal value, the enzyme activity is decreased as well. When the pH value far increases above the optimal value and becomes unsuitable, the enzyme activity is said to be denatured which makes it inactive.

Acidic solutions have more hydrogen ions which means more positive charges. These positive charges affect the charges of the amino acids inside the protein which render the enzyme more or less active depending on the optimal pH of the enzyme. Here are some examples of enzymes with their optimal and denatured pH.

Enzyme Optimal pH Denaturated pH
Pepsin 2 6-7
Amylase 7 11
Lactase 6.6-6.8 11
Catalase 7-11 13


pH has an effect on the gastric enzymes and hormones in the stomach

pH has an effect on the gastric enzymes and hormones in the stomach


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Frequently Asked Questions

Why does pH affect enzyme activity?

Because enzymes are proteins, their molecular structure is determined by interactions between the charges of the amino acids that compose the protein chains. These interactions take the form of hydrogen bonds, which are altered by pH. These positive charges impact the charges of the amino acids inside the protein, making the enzyme more or less active depending on the enzyme's optimum pH.

What is the effect of pH on enzyme activity?

Each enzyme has an optimal pH value. The optimum pH of an enzyme is the ideal pH value at which the enzymatic activity is greatest. When the pH falls below the ideal level, enzyme activity falls as well. When the pH level rises significantly over the ideal level and becomes inappropriate, the enzyme activity is said to be denatured, rendering it inactive and inert.

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