Final answer:
Increasing the substrate concentration initially increases the initial velocity of enzyme-catalyzed reactions, like with penicillinase, but eventually leads to a saturation point where additional substrate does not further increase the reaction rate.
Step-by-step explanation:
If the concentration of the substrate is low, increasing its concentration will generally lead to an increase in the initial velocity of an enzyme-catalyzed reaction, such as that involving penicillinase. However, as the substrate concentration continues to increase, a point is reached where the initial velocity of the reaction no longer rises. This is due to all the enzyme's active sites becoming occupied, which is known as saturation. Once saturation is achieved, additional substrate has no effect on the reaction rate because the enzyme can only process so much substrate at a time.
At low substrate concentrations, the reaction rate typically increases proportionally with the substrate concentration; for instance, doubling the concentration approximately doubles the reaction rate. Yet, this relationship is not linear indefinitely. At high concentrations of substrate, the relationship between substrate concentration and reaction rate follows a curvilinear trajectory, reaching a plateau where further increases in substrate do not yield a higher rate.
Graphically, when we plot velocity against substrate concentration, the curve obtained is hyperbolic, reflecting the initial linear increase in reaction rate with increased substrate levels, transitioning into a plateau phase as the enzyme approaches saturation. This concept is an essential part of understanding enzyme kinetics and the Michaelis-Menten equation, which describes the rate of enzymatic reactions.