Effect of [Substrate] and [Enzyme] on Km and Vmax?

[NSxortho]

This is in relation to the AAMC Sample B/B Q24 that asks "If the concentration of the transporter protein is increased, the transport affinity of L-alanine will:"
The answer is "Not change" as increasing the concentration of enzyme has no effect on Km (affinity).

So [enzyme] has no effect on Km, but it does change the Vmax right? proportionally I'm assuming?
What about [substrate]? How does it affect Km and Vmax?

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[theonlytycrane]

The enzyme and substrate have an affinity to one another depending on their chemical interactions. Maybe there is some h-bonding, electrostatic interactions, etc. But just because you add more enzyme into solution, the individual chemical interactions between an enzyme and substrate will not change. This also holds for adding more substrate.

Vmax is the maximum reaction rate of an individual enzyme. Adding more of an enzyme won't change each enzyme's max rate.

edit: See @aldol16's post below. I was thinking about kcat, not vmax. Vmax will increase if [E] changes.

 

[JustinM88]

This is in relation to the AAMC Sample B/B Q24 that asks "If the concentration of the transporter protein is increased, the transport affinity of L-alanine will:"
The answer is "Not change" as increasing the concentration of enzyme has no effect on Km (affinity).

So [enzyme] has no effect on Km, but it does change the Vmax right? proportionally I'm assuming?
What about [substrate]? How does it affect Km and Vmax?

Km = the [substrate] at (1/2)Vmax
^based on that definition, increasing the transporter protein shouldn't have any effect.
(equation version: Km = (Vmax[substrate]) / Vo)

Other important equation that does involve [Enzyme]:
Kcat = Vmax / [Enzyme]
In words, Kcat is the number of cycles catalyzed per second. It's easy to see this definition once you write out the units of Vmax and [Enzyme] on paper and cancel out the M on the top and bottom

 

[aldol16]

So [enzyme] has no effect on Km, but it does change the Vmax right? proportionally I'm assuming?

Yes, Vmax = kcat*[E]

What about [substrate]? How does it affect Km and Vmax?

It does not affect Vmax or Km.

 

[aldol16]

Vmax is the maximum reaction rate of an individual enzyme. Adding more of an enzyme won't change each enzyme's max rate.

Vmax is a maximum reaction velocity and happens when all of the enzyme's active sites are saturated with substrate. Therefore, adding more enzyme will proportionally change Vmax by the following relation: Vmax = kcat*[E]. We actually use Vmax as a proxy to measure enzyme concentrations when those concentrations are difficult to obtain by other means.

 

[NSxortho]

Vmax is a maximum reaction velocity and happens when all of the enzyme's active sites are saturated with substrate. Therefore, adding more enzyme will proportionally change Vmax by the following relation: Vmax = kcat*[E]. We actually use Vmax as a proxy to measure enzyme concentrations when those concentrations are difficult to obtain by other means.

This makes sense! thank you, and the others!