Question

3)   In enzyme kinetics why does the initial reaction rate (vo) resemble the steady state in living cells?  

4)   Also, in enzyme kinetics the Km value is an indicator of enzyme binding efficiency, is a low or high Km value indicative of better efficiency in living cells? Why?

5)   Consider competitive inhibitors. Why does their presence raise the Km value?

Answer 1

1. The initial rate of the formation of a product from an enzyme is also known as the initial velocity, or Vo, it is affected by the substrate concentration, [S].   The initial reaction rates often resemble the steady-state situation in living cells, because the substrates are usually replenished in a continuous manner and products are also removed in a continuous manner, therefore, maintaining stable concentrations of both substrate and product.

2. The Michaelis-Menton constant Km can be defined as the concentration of substrate at ½ Vmax. It is reported to be an inverse measure of its substrate affinity. A high Km denotes that a higher amount of substrate will be needed by the enzyme to reach a certain reaction speed. Therefore, an enzyme with a high Km value has lower binding affinity for its substrate. On the other hand, lower Km values indicate that lower amount of substrate will be needed by the enzyme to reach a certain reaction speed and the enzyme has higher binding affinity for its substrate. We can conclude that an enzyme with low Km value is a good enzyme.

3. Competitive inhibitors are structural analog of the normal substrate. The competitive inhibitors compete with substrate to bind to the active site of the enzyme. The inhibition can also be reversed if amount of substrate is increased. The increased substrate replaces the inhibitor from the active site. As the inhibition is reversible the Vmax remains constant. There is an increase in the Km value because increased amount of substrate is required to remove the inhibition.