Michaelis-Menten: Why does a low Km imply a strong affinity?

[BigToque]

E + S <> ES <> E + P

Km = (Kforward + Kcat) / Kreverse

(assuming Kcat is << 1)

Km = Kforward / Kreverse

I've gone through the equation, and can see how a high or low value of Km affects the value for V0, but when I look at the equation at the top (E + S <> ES <> E + P), I just don't see how having Kreverse being larger than Kforward implies that the enzyme has a greater affinity for the substrate.

To me, having Kreverse being >>> than Kforward (and thus a really small Km), the equation is saying that the reaction favors being in the E + S form, and basically tells me that the enzyme wants absolutely nothing to do with the substrate. It wants to get as far away from the substrate as possible.

Since I'm pretty sure Michaelis and Menten are correct, what am I not understanding?

 

[lxskllr]

Not really a fan of the KDE desktop, or QT styling in general. I much prefer GTK+

 

[Gibsons]

This might not help, it's been ages since I had to work the nuts and bolts of this stuff, but...

First remember Km is a concentration, not really a velocity. Don't think about the reaction so much, think about what the enzyme 'needs' in order to work. A high km only works well if there's a lot of substrate around, a lower km still works at lower concentrations.

edit: re-read your question, this probably won't help at all, sorry.

 

[BigToque]

Not really a fan of the KDE desktop, or QT styling in general. I much prefer GTK+

Lol, it took me a second...

I prefer GTK as well.

 

[CottonRabbit]

I'm pretty sure you just have the last equation flipped. Km = Kr/Kf

 

[Rezag3000]

From what I recall, there are several ways to answer your question. The one that I remember is as follows:

Km is the concentration of the substrate at which V = 1/2Vmax. This means that the lower Km is, the less substrate you need to reach 1/2Vmax. You can therefore conclude that if Km is lower, the enzyme-substrate affinity must be greater.

 

[Fayd]

I did non-linear regression of the Michaelis Menten data....and i still have no idea what it's supposed to be about.

 

[ecox1]

http://en.wikipedia.org/wiki/Michaelis–Menten_kinetics

"Km is the inverse of the enzymes affinity", or think of it as the enzymes K^-1

This would imply that an enzyme with a high K value, or high affinity would have a low value. If K=5 then Km=1/5 .

Best explanation I can come up with after being out of the class for 1 year, this part of Biochemistry sucked.