In an enzyme-catalyzed reaction with constant enzyme concentration, what occurs to the initial velocity (V₀) as more substrate is added?

• A. It decreases
• B. It remains the same
• C. It increases
• D. It fluctuates dramatically

Answer: (C)

In an enzyme-catalyzed reaction at constant enzyme concentration, the initial velocity (V₀) is directly related to the concentration of substrate available. According to Michaelis-Menten kinetics, as the concentration of substrate increases, V₀ also increases, because there are more substrate molecules available for the enzyme to bind to, leading to more enzymatic reactions occurring simultaneously.

At low substrate concentrations, there are many active sites on the enzyme available, and an increase in substrate concentration results in a proportional increase in the initial velocity. As more substrate is added, more enzyme-substrate complexes can form, driving up the rate of reaction until the enzyme becomes saturated.

When saturation is reached, the increase in V₀ begins to level off, but this saturation point is typically at relatively high substrate concentrations. Therefore, at the initial stages of adding more substrate, V₀ steadily increases.

This relationship highlights the importance of substrate concentration in influencing enzyme activity, reinforcing the idea that enzyme kinetics can initially correlate directly with substrate availability.