Catalytic Efficiency Definition
Catalytic efficiency measures how effectively an enzyme converts substrate to product. For enzymes following Michaelis-Menten kinetics, this efficiency is determined by combining the enzyme's turnover rate and its affinity for the substrate.
Key Kinetic Parameters
- $k_{Cat}$ (Turnover Number): Represents the maximum rate of catalysis per enzyme active site. It indicates how many substrate molecules one enzyme molecule can convert into product per unit time.
- $K_M$ (Michaelis Constant): Represents the substrate concentration at which the reaction rate is half of $V_{max}$. It often reflects the enzyme's affinity for its substrate; a lower $K_M$ suggests higher affinity.
Calculating Catalytic Efficiency
Catalytic efficiency is defined as the ratio of $k_{Cat}$ to $K_M$. This measure combines how fast the enzyme works ($k_{Cat}$) with the substrate concentration it requires to function effectively ($K_M$).
Formula: Catalytic Efficiency $\boldsymbol{=} \frac{k_{Cat}}{K_M}$
Significance of the Ratio
A higher value of $\frac{k_{Cat}}{K_M}$ indicates greater catalytic efficiency. This means the enzyme has a high turnover rate (large $k_{Cat}$) and/or binds strongly to its substrate (small $K_M$), allowing it to efficiently process the substrate even at low concentrations.
Therefore, the catalytic efficiency of an enzyme following Michaelis-Menten kinetics is given by the term $\frac{k_{Cat}}{K_M}$.
Important Questions from Enzyme Kinetics and Michaelis Menten Equation
- An enzyme (E) catalyzes the biochemical reaction $A \rightarrow B$ with $k_{cat}$ equal to $500 s^{-1}$. If the initial reaction velocity ($V_0$) is $10 \mu M.s^{-1}$ at the total enzyme concentration $[E_t]$ of 30 nM and substrate concentration $[A]$ of $40 \mu M$, the value of $K_m$ (in $\mu M$) is ________
Within the Michaelis-Menten framework, the ratio of $v_0/V_{max}$
when $[S] = 20 \times K_m$ is _________.
(Round off to two decimal places)
The enzyme $\alpha$-amylase used in starch hydrolysis has an affinity constant ($K_m$) value of $0.005$ M. To achieve one-fourth of the maximum rate of hydrolysis, the required starch concentration in mM (rounded off to two decimal places) is____.
An enzymatic reaction exhibits Michaelis-Menten kinetics. For this reaction, on doubling the concentration of enzyme while maintaining [S] >> [$E_o$],
- In an assay of the type II dehydroquinase of molecular mass 18 kDa, it is found that the $V_{max}$ of the enzyme is $0.0134 \ \mu mol.min^{-1}$ when $1.8 \ \mu g$ enzyme is added to the assay mixture. If the $K_m$ for the substrate is $25 \ \mu M$, the $k_{cat}/K_m$ ratio will be ____________________ $\times 10^4 \ M^{-1}.s^{-1}$.
