GATE2016-44

Question

The activity of lactate dehydrogenase can be measured by monitoring the following reaction: $$\text{Pyruvate} + \text{NADH} \rightarrow \text{Lactate} + \text{NAD}^+$$ The molar extinction coefficient of NADH at $340$ nm is $6220 \: M^{-1} \cdot cm^{-1}. NAD^+$ 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 $0.14  \: \text{min}^{-1}$. The specific activity of the enzyme will be __________ $\mu \text{mol.min}^{-1}.mg^{-1}$