Question

5. What is the significance of a low value or high value for Km in terms of how an enzyme works? For example: compare 1x10^-10 M to 1x10^-3 M.   (4 points)

Answer 1

1. Km value is substrate concentration (expressed in moles/L) at half-maximal velocity
2. It denotes that 50% of enzyme molecules are bound with substrate molecules at that particular substrate concentration
3. Km is independent of enzyme concentration. If enzyme
concentration is doubled, the Vmax will be double.
But the at ½ Vmax, Km will remain exactly same. In other words, irrespective of enzyme concentration, 50% molecules are bound to substrate at that particular substrate concentration.
4. Km is the signature of the enzyme. Km value is thus a constant for an enzyme. It is the characteristic feature of a particular enzyme for a specific substrate.
5. The affinity of an enzyme towards its substrate is inversely related to the dissociation constant, Kd for the enzyme-substrate complex.

Therefore, the smaller the tendency for the dissociation of the complex, the greater is the affinity of the enzyme for the substrate.
6. Km denotes the affinity of enzyme for substrate. The lesser the numerical value of Km, the affinity of the enzyme for the substrate is more.

thus, enzyme with Km 1x10^-10 M kas higher affinity towards substrate than enzyme with Km 1x10^-3 M.