The velocity of a reaction is 40 µM/min at a substrate concentration of 1.5 mM. The enzyme is known to reach maximal velocity at 220 µM/min. What would the velocity be at a substrate concentration of 5 mM?
We know that,
V = (Vmax × [S]) ÷ (KM + [S])
Where,
V = Velocity of reaction at particular concentration of substrate, [S]
Vmax = maximal velocity = 220 µM/min
[S] = Substrate concentration
Km = Michaelis constant (a measure of enzyme/substrate affinity)
For solving this, first finding the Km value when substrate concentration is 1.5 mM
V1 = 40 µM/min
[S1] = 1.5 mM
Vmax = 220 µM/min
V = (Vmax × [S]) ÷ (Km + [S])
40 = (220 × 1.5) ÷ ( Km + 1.5)
40Km + 60 = 330
40Km = 330 - 60
Km = 270/40 = 6.75 mM
Now, putting Km in the second reaction where concentration of substrate is 5 mM.
[S] = 5 mM, we have to find V = ?
V = (220 × 5) ÷ (6.75 + 5)
V = 1100/ 11.75
V = 93.62
Thus velocity at substrate concentration 5 mM is 93.63 µM/min.
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