The rate of an enzyme catalysed reaction levels off at high substrate concentration because
Correct answer: B. all the active sites are occupied, so the enzyme is saturated
- A. the substrate begins to inhibit the enzyme
- B. all the active sites are occupied, so the enzyme is saturated
- C. the enzyme is denatured by the substrate
- D. the products stop the reaction
Explanation
Once every active site is engaged, adding more substrate cannot increase the rate, and the plateau reached is Vmax. At that point the enzyme concentration rather than the substrate is limiting, so adding more enzyme would raise the rate again. This saturation behaviour is one of the clearest differences between enzymes and inorganic catalysts.
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About Enzymes as Biocatalysts
Enzymes are protein or RNA biocatalysts that lower activation energy without being consumed, and their active sites bind specific substrates. The topic covers the lock and key and induced fit models, effects of temperature, pH and substrate concentration, cofactors, enzyme specificity, and competitive versus non-competitive inhibition.
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