An enzymatic reaction exhibits Michaelis-Menten kinetics. For this reaction, on doubling the concentration of enzyme while maintaining [S] >> [$E_o$],
$K_m$ will remain the same but $V_{max}$ will increase.
Enzyme Kinetics Explanation
Michaelis-Menten kinetics describes the rate of enzymatic reactions. Key parameters are $K_m$ and $V_{max}$. The reaction follows the equation:
$v = \frac{V_{max}[S]}{K_m + [S]}$
where $v$ is the reaction velocity, $[S]$ is the substrate concentration, $K_m$ is the Michaelis constant, and $V_{max}$ is the maximum reaction velocity.
Enzyme Concentration Effects
The question asks about the effect of doubling the enzyme concentration ($[E_o]$) while keeping $[S] \gg [E_o]$.
- Effect on $K_m$: The Michaelis constant ($K_m$) reflects the enzyme's affinity for its substrate. It is generally independent of enzyme concentration. Doubling $[E_o]$ does not alter the intrinsic binding properties of the enzyme. Therefore, $K_m$ remains unchanged.
- Effect on $V_{max}$: The maximum velocity ($V_{max}$) is directly proportional to the total enzyme concentration ($[E_o]$) and the turnover number ($k_{cat}$), according to the relation $V_{max} = k_{cat}[E_o]$. When the enzyme concentration is doubled, $V_{max}$ also doubles, assuming $k_{cat}$ remains constant.
Thus, doubling the enzyme concentration leaves $K_m$ unchanged but increases $V_{max}$.
Important Questions from Enzyme Kinetics and Michaelis Menten Equation
- The catalytic efficiency of an enzyme following Michaelis-Menten kinetics is defined by
You are characterizing a new enzyme isolated and purified in the laboratory. If the maximum velocity of the enzyme is $1800 \text{ } \mu moles \text{ L}^{-1} \text{min}^{-1}$ and the total concentration of the enzyme in the reaction mixture is $1.5 \mu \text{M}$, then the turnover number of the enzyme is _______ $\text{s}^{-1}$. (answer in integer)
You have purified an enzyme using a series of chromatographic methods. It was observed that a $10 \mu \text{ g mL}^{-1}$ of this purified enzyme converted $10 \text{ mM}$ substrate per hour at 25$^{\circ}$C and pH 7. Its specific activity is _______ $\text{IU } \mu\text{g}^{-1}$. (rounded off to three decimal places)
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 activity of lactate dehydrogenase can be measured by monitoring the following reaction:
Pyruvate + NADH $ \longrightarrow $ Lactate + $NAD^+$
The molar extinction coefficient of NADH at 340 nm is $6220 \ M^{-1}.cm^{-1}$. $NAD^+$ does not absorb at this wavelength. In an assay, $25 \ \mu L$ of a sample of enzyme (containing $5 \ \mu g$ protein per mL) was added to a mixture of pyruvate and NADH to give a total volume of 3 mL in a cuvette of 1 cm pathlength. The rate of decrease in absorbance at 340 nm was $0.14 \ min^{-1}$. The specific activity of the enzyme will be ____________________ $ \mu mol.min^{-1}.mg^{-1}$.
