Question

The catalytic efficiency of two different enzymes can effectively be compared by the

• A. K${}_m$ value
• B. pH optimum value
• C. molecular size of the enzyme
• D. temperature optimum value

Answer 1

The correct option is A K${}_m$ value

The catalytic efficiency of two different enzymes can be compared by their K${}_m$ values. The K${}_m$ or the Michaelis-Menten constant refers to the concentration of substrate at which the reaction reaches half its maximum velocity. K${}_m$ indicates the affinity of the enzyme for its substrate.
A high K${}_m$ value indicates low affinity while low K${}_m$ value indicates a high affinity for the substrate.
A higher affinity for the substrate corresponds to higher efficiency of enzymes, since high affinity ensures greater amount of substrate-enzyme binding and product formation. Small
K${}_m$ also suggests that an enzyme is able to tightly bind with the substrate.

Different enzymes have different pH optima. pH alone cannot be used to compare the efficiency of two enzymes. Some enzymes function in acidic environments while others in an alkaline environment.

Molecular size of the enzyme generally has got little to do with its efficiency.
Same is the case with temperature. Being proteinaceous, the enzymes are generally thermolabile (temperature-sensitive) in nature. They generally work over a narrow range of temperature. At lower temperatures, enzymes become inactivated and at higher temperatures, they may get denatured. However, certain enzymes are very resistant to high temperatures. For example, Taq polymerase obtained from Thermus aquaticus has its temperature optima at 72-degree celsius. Temperatures optima can vary between enzymes and cannot be used as a sole criterion for comparing the efficiency of two enzymes.