23 out of 91
Km of an enzyme is : (DNB Dec 2010)
|B||The normal physiological substrate concentration|
|C||The substrate concentration at half maximal velocity|
|D||Numerically identical for all isozymes that catalyze a given reaction.|
Ans. C The substrate concentration at half maximal velocity
- Km is Michaelis Menten constant, it is the characteristic of an enzyme and a particular substrate and it reflects the affinity of the enzyme for that substrate.
- Km is numerically equal to the substrate concentration at which the reaction velocity is equal to 1/2 Vmax.
- Numerically, small Km reflects a high affinity of the enzyme for substrate because a low concentration of the substrate is needed to half saturate the enzyme.
- A numerically large Km reflects a low affinity of enzyme for substrate because a high concentration of substrate is needed to half saturate the enzyme.
- The rate of the reaction is directly proportional to the enzyme concentration at all substrate concentration.
- First order reaction - when substrate concentration is much less than Km, the velocity of the reaction is roughly proportional to the substrate concentration. The rate of the reaction is then said to be of first order.
- Zero order reaction - When substrate concentration is much greater than Km, the velocity is constant and equal to Vmax. The rate of reaction is then independent of substrate concentration and said to be of the zero order.