The following statements are being made to define the Michaelis constant (Km). It is:
A. Independent of enzyme concentration [E] and substrate concentration [S]
B. Equal to the dissociation constant when the [ES] complex dissociates more rapidly than product formation
C. Equal to the dissociation constant when product formation is more rapid than [ES] complex dissociation
D. An intrinsic property of an enzyme and does not depend on pH, temperature, and ionic strength

Which one of the following combination of statements is correct?

Correct option is A

Explanation-

​Statement A: "Independent of enzyme concentration [E] and substrate concentration [S]" - CORRECT
_m is a constant derived from intrinsic enzyme kinetics. It is independent of the concentrations of enzyme and substrate. It reflects the affinity of the enzyme for its substrate.

Statement B: "Equal to the dissociation constant when the [ES] complex dissociates more rapidly than product formation" - CORRECT

​$$K_m = \frac{k_{-1} + k_2}{k_1}$$

$$\text{If } k_2 \ll k_{-1} \text{ (product formation is slower than ES breakdown),}$$ $$\text{then } K_m \approx \frac{k_{-1}}{k_1} = K_d \text{ (the dissociation constant of ES).}$$

Hence, this statement is valid under specific conditions.

​Statement C: "Equal to the dissociation constant when product formation is more rapid than [ES] complex dissociation" - INCORRECT

$$\text{If product formation is \textbf{faster} than ES dissociation (i.e. } k_2 \gg k_{-1} \text{),}$$ $$\text{then } K_m \approx \frac{k_2}{k_1}, \text{ not equal to } K_d = \frac{k_{-1}}{k_1}.$$

​​​Therefore, this statement is incorrect.

Statement D: "An intrinsic property of an enzyme and does not depend on pH, temperature and ionic strength" - INCORRECT

_m  is intrinsic to a given enzyme-substrate pair, but it can vary with changes in pH, temperature, and ionic strength, as these can affect enzyme structure and binding.

​Final Answer: Option a — A and B only ( since statement A and B shows a correct combination)

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