An enzyme with a low Km value for its substrate
Correct answer: C. has a high affinity for that substrate, reaching half its maximum rate at a low concentration
- A. reaches Vmax only at very high substrate concentrations
- B. has been irreversibly inhibited
- C. has a high affinity for that substrate, reaching half its maximum rate at a low concentration
- D. is working below its optimum temperature
Explanation
Km is the substrate concentration at which the reaction runs at half of Vmax, so a small Km means the active sites are half occupied even when substrate is scarce, which is the definition of high affinity. This is why Km is used to compare how tightly different enzymes hold the same substrate. Vmax measures how fast the enzyme works when saturated and is a separate quantity.
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About Factors Affecting Enzyme Action
Enzyme activity changes with temperature, pH, substrate concentration and enzyme concentration because these factors affect molecular collisions and the active site. Questions also examine optimum conditions, denaturation and inhibition, while distinguishing a fall in activity caused by unsuitable conditions from permanent enzyme damage.
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