Step I Km and Vmax

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cosine

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How do you guys remember if the increase or decrease in the presence of a competitive and noncompetitive inhibitor. I crammed it in my first year and never really understood the concept behind it. anyone care to explain?
 
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the way i remember is this: in the business world competitors(eg. coke and pepsi, apple and microsoft) always cross each other (you get an "X"). So if you draw the graph you can tell Km increases and Vmax stays the same since its the middle of the "X". hope this helps you
 
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First here are some definitions


Km - Substrate amount that is needed to reach 1/2 of Vmax

Vmax - Maximum velocity of reaction


Competitive vs Noncompetitive


Competitive would increase Km but Vmax would be the same (since it is is competing you would need to increase more Km)

Noncompetitive Km would be the same but Vmax would be lowered (since it is not binding to the active site)


Please feel free to correct me.

http://www.chembio.uoguelph.ca/educmat/Chm258/enzplots.htm
 
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On a lineweaver burk plot, if the lines cross, it is competitive inhibition. C= cross, competitive.

If there is no cross, it is non competitive. NC= no cross, non competitive.
 
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Captopril said:
On a lineweaver burk plot, if the lines cross, it is competitive inhibition. C= cross, competitive.

If there is no cross, it is non competitive. NC= no cross, non competitive.
Click to expand...

Thanks guys I just had a question on kaplan q bank and blew it up I would have gotten it rite if I read this thread a little earlier. I never wanted to put that thing in my head.
One more thing that I saw on the explanation that may be helpful. Since everything is inversed on the curve, an increase in anything (Km, Vm and S ) will happen with a convergence to zero. For example since Vm ( I mean 1/Vm ) is reppresented on the vertical axis, a convergence downto the pont zero mean an increase in Vm. Same thing apply to Km (represented on horizontal left) and S on horizontal right
 
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cosine said:
How do you guys remember if the increase or decrease in the presence of a competitive and noncompetitive inhibitor. I crammed it in my first year and never really understood the concept behind it. anyone care to explain?
Click to expand...

the concept is this
a competitive inhibitor is going to try and bind in the exact same spot as the substrate. So, if the inhibitor is bound it will make it more difficult for the substrate to bind (which will change Km, since Km reflects binding affinity)
In a non competitive inhibitor (for the simplistic purposes of how we need to understand it) it binds to a totally different site on the enzyme, so theoretically the substrate could still get into the active site and bind (thus not affectin Km)
for Vmax, since the competitive inhibitor and sustrate are competing for that same site, whoever is in higher amount "wins" thus you can "compete out" the competitor..so you can still get to your vmax
with a non competitive inhibitor, it functions by altering the activitiy of the enzyme, so while it binds to a different site (and thus does not affect Km) it will alter Vmax, since no matter how much substrate you add wont "push off" the inhibitor
now for Km itself, always remember the lower the number the better the affinity. On Lineweaver burke plots you are looking at the inverse of Km at the x intercept, and the 1/Vmax on the y intercept, this a higher Km will be a smaller number on X, etc
hope this helps
 
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