Enzyme Kinetics

[PeanutButter1]

Hi all, 

 

I encountered a question on my MCAT regarding Kd (binding dissociation constant), and was thrown off as I had never heard of this before (except in the context of Ka and Kb and Ksp ... I assume it's similar to these constants?). Anyway, I only studied Km with respect to enzyme kinetics. Is Km=Kd? If not, how is it different? I know <<<Km means better enzyme affinity and more effective/efficient enzyme. But what about Kd? 

 

Also - random question, can someone confirm - is the ox state of Fe in Na4(FeBr6) equal to +2? Thanks in advance

[Artier]

No Km and Kd are two separate parameters as Km has to do with the kinetics of the system while Kd has to do with its thermodynamics.

 

Kd is just an equilibrium constant K used to describe the dissociation of large molecules. (Read the wiki page on it, it's pretty simple to understand:https://en.wikipedia.org/wiki/Dissociation_constant)

 

As such, Kd tells you nothing about enzyme kinetics.

Yes, the ox state of Fe in that molecule is +2.
 

[PeanutButter1]

No Km and Kd are two separate parameters as Km has to do with the kinetics of the system while Kd has to do with its thermodynamics.

 

Kd is just an equilibrium constant K used to describe the dissociation of large molecules. (Read the wiki page on it, it's pretty simple to understand:https://en.wikipedia.org/wiki/Dissociation_constant)

 

As such, Kd tells you nothing about enzyme kinetics.

 

Yes, the ox state of Fe in that molecule is +2.

 

 

 

Thank you! Kind of confused about whether a large or a small Kd is "better" - specifically, I can see if the number if larger, it would be a good thing because that means high product turn over... but elsewhere I read that a smaller Kd means the enzyme function is better than an enzyme with higher Kd value? 

 

Thanks again

 

EDIT: I think I had it backwards... by dissociate it means dissociate BACK to reactant and substrate i.e. Kd = [reactant] / [product] ... therefore a SMALLER Kd is good... where as Ka (association constant) would be [product]/[reactant] and HIGHER Ka is better

[Artier]

I PM'd you.