Question

Adding concentrated strong base to a solution containing an enzyme often reduces enzyme activity to zero. In addition to causing protein denaturation, which of the following is another plausible reason for the loss of enzyme activity? (A) Enzyme activity, once lost, cannot be recovered. (B) The base can cleave peptide residues. (C) \(\quad\) Adding a base catalyzes protein polymerization. \((\mathrm{D})\) Adding a base tends to deprotonate amino acids on the surface of proteins.

Short answer

Option (D) is most plausible because adding a base deprotonates amino acids on the enzyme's surface.

Step-by-step solution

Understand the Problem and Options

Read the question carefully to determine what it is asking about enzyme activity reduction when a strong base is added. The options provided are potential reasons explaining why the activity diminishes.

Recognize the Effects of Bases on Enzymes

Recall that a base can affect enzymes in different ways: protein denaturation, peptide bond cleavage, polymerization, or deprotonation of amino acids. Write down these effects for better visualization.

Evaluate Each Option

Analyze each given option: (A) Irreversible loss of enzyme activity - This is not necessarily true as some enzymes can refold or be reconstituted. (B) Peptide bond cleavage - Strong bases can indeed catalyze the breaking of peptide bonds. (C) Catalyzed polymerization - This is less likely as it is not a common reaction for bases. (D) Deprotonation of amino acids - Strong bases often cause deprotonation, affecting enzyme structure and function adversely.

Choose the Most Plausible Reason

Evaluate the findings from Step 3. The most plausible answer for loss of enzyme activity, besides protein denaturation, is deprotonation of amino acids as it directly impacts protein structure and function (Option (D)).

Key concepts

protein denaturation

Protein denaturation refers to the process where a protein loses its natural structure. Proteins have a specific three-dimensional shape which is key to their function. When this structure is disrupted, the protein can no longer perform its biological function.
Denaturation can be caused by heat, pH changes, and chemicals like strong bases. When you add a concentrated strong base to a protein solution, it can disrupt the hydrogen bonds and other interactions that maintain the protein’s structure. This leads to the protein unfolding and losing its activity. A denatured enzyme cannot bind to its substrate effectively, which results in a loss of enzyme activity.

peptide bond cleavage

Peptide bond cleavage involves the breaking of the bonds between amino acids in a protein. Proteins are made up of long chains of amino acids held together by peptide bonds.
When a strong base is added to a protein solution, it can attack these peptide bonds, breaking them and thus fragmenting the protein. This process effectively destroys the protein’s primary structure. An enzyme, which relies on its sequence of amino acids and their arrangement to function, will lose its activity if these bonds are broken. Such cleavage usually leads to irreversible loss of enzyme function.

amino acid deprotonation

Amino acid deprotonation occurs when the amino acids that make up proteins lose a proton from their side chains or backbone. Enzymes have specific functional groups that need to remain protonated to maintain the enzyme’s structure and function.
Adding a strong base to the solution raises the pH and can lead to deprotonation of these amino acid groups. When amino acids lose protons, this alters the charge and shape of the enzyme, possibly unfolding it or disrupting its active site. This alteration can hinder the enzyme's ability to catalyze reactions, significantly reducing or completely stopping its activity.

base effects on enzymes

Bases can have multiple effects on enzymes, beyond just denaturation and deprotonation. Here are some effects:

• Disruption of Ionic Bonds: Enzymes often rely on ionic bonds between amino acids to maintain their structure. Bases can disrupt these bonds, leading to structural changes.
• Inactivation: Strong bases can interact with the enzyme's active sites, blocking substrate binding or interfering with the reaction mechanism.
• Altering Protein-Solvent Interactions: Bases can change how proteins interact with the solvent, potentially leading to precipitation and loss of function.

Thus, the addition of a strong base can severely impact enzyme activity through multiple pathways, making it crucial to maintain enzyme solutions at appropriate pH levels to preserve their activity.