Question

Michaelis Menten Constant $(K_m)$ is equal to

• A. the rate of reaction
• B. the rate of enzymatic activity
• C. substrate concentration at which the reaction attains half of its maximum velocity
• D. substrate concentration at which the rate of reaction is maximum

Answer 1

Answer: (C)

$K_m$ or the Michaelis-Menten constant is defined as the substrate concentration (expressed in moles/l) at which half-maximum velocity in an enzyme catalysed reaction is achieved. It indicates that half of the enzyme molecules (i.e. $50\%$) are bound with the substrate molecules when the substrate concentration equals the Km value. It was given by Leonor Michaelis and Maud Menten $(1913)$. $K_m$ value is a characteristic feature of a given enzyme. It is a representative for measuring the strength of $ES$ complex. A low $K_m$ value indicates a strong affinity between enzyme and substrate, whereas a high $K_m$ value reflects a weak affinity between them. For majority of enzymes, the $K_m$ values are in the range of $10^{-5}$ to $10^{-2}$ moles.