Competitive, non-competitive, irreversible and allosteric inhibitors

[nashaiy]

So for enzyme regulation, the MCAT requires us to know about competitive, non-competitive, irreversible and allosteric inhibitors. I understand the basic concepts for all of these but was wondering if someone could verify the following:

1. Competitive inhibitors: since these can be overcome with increased substrate concentration, Vmax is not changed but Km is increased (i.e. more substrate needed to reach 0.5Vmax). Also, enzyme affinity for the substrate stays the same (is this right?).

2. Non-competitive inhibitors: since these bind to another site other than the active site, they cannot be overcome by adding substrate. Thus, Vmax is decreased. What happens to Km? I would guess it would stay the same as Vmax is reduced as well but I'm unclear on this. Also, enzyme affinity for the substrate is lowered (correct?).

3. Irreversible inhibitors: covalently bond to the enzyme altering it's active site. Does this have the same effect as non-competitive inhibitors in terms of Vmax and Km? How are these factors affected?

4. Allosteric inhibitors: I don't understand how these are different than non-competitive inhibitors.

Anything else about enzyme inhibitors that we have to know that you think would be relevant, please let me know. Any help would be appreciated!

Thanks!

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[circulus vitios]

It is important to note that, while all non-competitive inhibitors bind at allosteric sites-- i.e. any site on the enzyme other than its active site-- not all inhibitors that bind at allosteric sites are non-competitive inhibitors.[1] [2] In fact, allosteric inhibitors may act as competitive, non-competitive, or uncompetitive inhibitors.http://en.wikipedia.org/wiki/Non-competitive_inhibition#cite_note-NIH_Inhibition-0

http://en.wikipedia.org/wiki/Non-competitive_inhibition#cite_note-NIH_Inhibition-0

EK mentions that saturation kinetics aren't tested on the MCAT.

Competitive inhibitors: Raise Km, do not change Vmax.
Non-competitive inhibitors: Do not change Km, lower Vmax.
Uncompetitive inhibitors: Lower Km, lower Vmax.

 

[Mornhavon]

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