How do Rm and Ks change with cell concentration? I have a few questions about ce
ID: 90943 • Letter: H
Question
How do Rm and Ks change with cell concentration?
I have a few questions about cells immobilized in beads:
Assuming that the bulk substrate concentration remains the same, how do Rm and Ks change if the cell concentration within the beads is decreased?
How do Rm and Ks change if the cell concentration within the beads are increased?
(Answers to choose from are increase/decrease/remain the same. I've been told that Rm does not increase with cell concentration, but it's difficult for me to understand since Vmax is dependent on enzyme concentration, and the same concept would seem to be true for cells, please include an explanation with your answer so I can understand! Thank you!)
Explanation / Answer
Km is the concentration of substrate at which the enzyme will be running at half the speed. In a monomeric enzyme with a single active site, the Km is independent of the enzyme concentration. That is, the concentration at which the rate is half-maximum, or Vmax/2. (Vmax is the rate and has dimensions of concentration/time). Vmax is directly proportional to the enzyme concentration [E]. So, if [E] is varied Vmax will also vary in tandem. This will not affect Km which remains the substrate concentration at which the rate is exactly Vmax/2.
If the amount of enzyme is doubled then the Vmax increases. However, if the measurement is not done under the right conditions for Michaelis-Menten kinetics, the Km may appear to vary with the enzyme concentration. The enzyme concentration must be much lower then the substrate concentration, and one must measure the initial rate of the reaction. If the enzyme concentration is too high, these conditions may be violated. The rate of mass flow (Rm) does not change with the increase with cell concentration, because the flow is not associated with the change in enzyme concentration.
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