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Difficulty: HardAnimal Nutrition and Digestive System

An enzyme sample of pepsin extracted from mammalian gastric juice was incubated at 0∘C0^\circ\text{C} with a protein substrate at pH 2.0\text{pH } 2.0 for two hours, during which no protein hydrolysis occurred. If the mixture is subsequently warmed to 37∘C37^\circ\text{C} while maintaining pH 2.0\text{pH } 2.0, which of the following outcomes and explanations is correct?

  1. Protein digestion proceeds normally because 0∘C0^\circ\text{C} causes temporary inactivation rather than permanent denaturation of the enzyme.Answer
  2. B
    No protein digestion occurs because exposure to 0∘C0^\circ\text{C} permanently denatures the active site of the pepsin molecules.
  3. C
    Protein breakdown occurs rapidly into glucose and amino acids via saprophytic extracellular secretion.
  4. D
    Digestion occurs only if the pH\text{pH} is adjusted to neutral 7.07.0 to compensate for thermal shock.

Answer

Protein digestion proceeds normally because freezing or low temperature causes temporary inactivation rather than permanent denaturation of the enzyme.
Low temperature (0∘C0^\circ\text{C}) reduces kinetic energy, leading to temporary inactivation of pepsin without damaging its 3D active site conformation. When returned to the body temperature (37∘C37^\circ\text{C}) under its optimal acidic environment (pH 2.0\text{pH } 2.0), the enzyme regains kinetic energy and successfully catalyzes the breakdown of proteins into peptides.

Step-by-Step Solution

1
Analyze the impact of low temperature (0∘C0^\circ\text{C}) on enzyme kinetics.
Low temperatures decrease the kinetic energy of reactant molecules, causing pepsin to become temporarily inactive.
Cold temperatures reduce molecular collision rates but do not disrupt the non-covalent bonds maintaining the enzyme's tertiary structure.
2
Evaluate the effect of returning the system to optimal temperature (37∘C37^\circ\text{C}) at optimal acidic pH 2.0\text{pH } 2.0.
The enzyme regains full catalytic potential as kinetic energy increases, leading to successful substrate binding.
Since denaturation occurs only at high thermal thresholds, warming restores full activity.

Key Concept

Effect of temperature and pH on digestive enzyme kinetics (Inactivation vs Denaturation)
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Topics

Animal Nutrition and Digestive System

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