Question

1. In your own words, describe what is the VMAX of an enzyme.

2. What would be the effect of adding more substrate to a reaction on the VMAXof the reaction?

3. What would be the effect of adding more enzyme to a reaction on the VMAX of the reaction?

4. In your own words, describe the what is KM of an enzyme.

5. In your own words, describe what is the specific activity of an enzyme.

6. Why is it necessary to track the absorbance over time of reactions using increasing concentrations of substrate in order to determine VMAX and KM?

7. Why only take the 0 and 1 minute timepoints into consideration for a Michaelis-Menten plot?

Answer 1

Answer 1. Vmax plays important role in enzyme action. Increase the substrate concentration indefinitely doesn't increase rate of an enzyme catalyzed reaction beyond certain point. This point is reached when there is enough substrate molecules to completely saturate the active site of an enzyme. Vmax reflects how fast enzyme can catalyze reaction.  

Answer 2. As the concentration of substrate increase, the enzyme becomes saturated with substrate. Adding more substrate will not affect the rate of the reaction to any significant effect. The rate of reaction when the enzyme is saturated with substrate is maximum rate of reaction.

Answer 3. Vmax obviously increases when the enzyme concentration is changed because of the amount of enzyme affects the rate of turnover given sufficient substrate.  

Answer 4. Km is the concentration of substrates when the reaction reaches half of Vamx. A small Km indicates high affinity since it means the reaction can reach half of the Vmax in a small number of substrate concentration. This small Km will approach Vmax more quickly than high Km value.  

Answer 5. Specific activity is a term used to measure the rate of reaction of an enzyme with a substrate. Specific enzyme activity is a measure of the purity of an enzyme solution and is quoted as units/mg. Measures purity of an enzyme solution and used in protein isolation methods to indicate the percentage of purification.