. An enzyme has a KM of 8µM in the absence of a competitive inhibitor and an apparent KM of 12 µM in the presence of 3µM of inhibitor. Calculate Ki .
To calculate Ki, we need to use the equation for the apparent Km in the presence of a competitive inhibitor:
Apparent Km = Km * (1 + [I] / Ki)
Where:
- Apparent Km is the Km value in the presence of the inhibitor
- Km is the Km value in the absence of any inhibitor
- [I] is the concentration of the inhibitor
- Ki is the inhibition constant of the inhibitor
In this case, we know the following values:
- Km = 8 µM
- Apparent Km = 12 µM
- [I] = 3 µM
Plugging in these values into the equation, we get:
12 µM = 8 µM * (1 + 3 µM / Ki)
To solve for Ki, we can rearrange the equation:
1 + 3 µM / Ki = 12 µM / 8 µM
1 + 3 µM / Ki = 1.5
3 µM / Ki = 0.5
Ki = 3 µM / 0.5
Simplifying further:
Ki = 6 µM
Therefore, the Ki value for this enzyme inhibitor is 6 µM.