Enzyme Activity Calculation in Katal
Enzyme activity quantifies the rate at which an enzyme converts substrate into product. The standard unit for enzyme activity is the Katal (kat), defined as one mole of substrate transformed per second.
Calculating Enzyme Activity Rate
The problem states that the enzyme converts 420 µmoles of substrate in one minute. We need to calculate this rate in Katals.
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Convert substrate amount to moles:
Amount = 420 µmoles
Since 1 µmole = $ 1 \times 10^{-6} $ moles, the amount is:
Amount = $ 420 \times 10^{-6} $ moles
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Convert time to seconds:
Time = 1 minute
Since 1 minute = 60 seconds, the time is:
Time = 60 seconds
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Calculate the reaction rate:
Rate = Amount converted / Time taken
Rate = $ \frac{420 \times 10^{-6} \text{ moles}}{60 \text{ seconds}} $
Rate = $ 7 \times 10^{-6} $ moles/second
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Express rate in Katals:
The rate calculated is $ 7 \times 10^{-6} $ moles/second, which is equal to $ 7 \times 10^{-6} $ Katals.
The question asks for the activity in the format '__________ $ \times 10^{-6} $ Katal'.
Therefore, the missing value is 7.
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}$.
