In a reaction mixture of enzyme keeping the enzyme concentration and other conditions constant only substrate concentration is changed. The enzyme activity to corresponding substrate concentrations are given below:
Substrate concentration in mM: 2, 5, 10, 15, 20
Enzyme activity in IU: 15, 25, 50, 56, 58
On the basis of the above observation table, the second-order reaction started after the first-order reaction occurred up to a substrate concentration of:
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First-order: V \(\propto\) [S] (at low [S]).
Zero-order: V = Vmax (at high [S]).
Michaelis-Menten kinetics describes this.
Step 1: Understanding the Concept:
Enzyme kinetics follows different orders at different substrate concentrations.
At low substrate concentration, first-order kinetics is observed. Step 2: Key Formula or Approach:
In first-order kinetics, velocity is directly proportional to substrate concentration.
In second-order kinetics, velocity becomes independent of substrate concentration. Step 3: Detailed Explanation:
Data:
[S] = 2 mM, V = 15 IU.
[S] = 5 mM, V = 25 IU.
[S] = 10 mM, V = 50 IU.
[S] = 15 mM, V = 56 IU.
[S] = 20 mM, V = 58 IU.
From 2 mM to 5 mM, V increases proportionally.
From 5 mM to 10 mM, V increases but not proportionally.
From 10 mM onwards, V increases very slowly (approaches Vmax).
Thus, first-order reaction occurs up to 5 mM.
After 5 mM, the reaction approaches zero-order kinetics. Step 4: Final Answer:
The second-order reaction started after first-order up to 5 mM.
Hence, the correct option is (B).
