mjl1717
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Can anyone briefly explain Lineweaver Burke?
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| mash
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plot of 1/V0 vs 1/[S]----straight line
1/V0= Km/Vmax[S] +1/Vmax
intercept on X axis ----1/Km
intercept on Y axis---1/Vmax
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| mjl1717
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Ok Mash you explained it mathematically, which I knew you could but could you explain it verbally or in words.
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| mash
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i ll try... in michaelis menton, we plot V0 vs [S],and we get a hyperbola..
At very high substrate conc[S] , it becomes difficult to get Vmax(bcoz of gradual upward slope)
lineweaver is reciprocal of michaelis menton,where we plot 1/Vo vs 1/[s]
1) 1/Vmax is where the st line intercepts Y axis..
-1/Km is where the st line intercepts X axis
2) inhibitors always lie above the st line on rt side of Y axis
competitive inh--Km is increased and Vmax is the same-- line will intercept X axis on the rt side of control
non comp inh--Km is constt and V max will decrease --line will intercept X axis at the same pt as control
3) line below the control represents addition of an activator
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| mjl1717
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Great! 
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| Malaysian
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Hi Mash good explnation I hope you can help me out in this aspect of Biochemistry too.
Could you explain in a logical manner as to how and why the competitive and non-competitive inhibitors change Vmax and Km.
What role an activator has in changing these values?
You mentioned in your explanation that anything above the control's line is considered an inhibitor.But doesn't an inhibitor which is non-competitive lie below the control line???Am confused here.
Apart from inhibitors and activators.....can the boards ask any other sort of 'substance' to interpret when it comes to the michelis menton/Lineweaver Burke graph??
Thanks in advance.
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| mash
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allosteric effectors r different frm inhibitors
allosteric effectors may be positive or negative effectors
curve is sigmoid (as compared to parabola in case of michaelis menton or straight line in case of lineweaver)
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| mjl1717
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Mathematicians like Copernicus, Galileo and Mash would probably prefer the double reciprocal plot or L.B. because it can determine Vmax at high sustrate concentrations.(As Mash says because of gradual upward slope
in Michaelis Menton)
1)Most enzymes exhibit Michaelis Menton kinetics-hyperbola (myoglobin)
Allosteric enzymes exhibit the sigmoid curve (hemoglobin)
2)When [S] is much greater then Km, the velocity is equal to Vmax.The rate of reaction isindependent of substrate conc. and said to be 0 order with respect to substrate conc.
When [S] is much less then Km the velocity of the reacion is proportional
to the substrate conc. The rate of reaction is said to be first order with respect to substrate conc.
3)An example of an irreversible inhibitor would be the covalent bonding of
acetylcholinesterase! [An inhibitor diminishes velocity]
4)1/V0=Km/Vmax[S]+1/Vmax
5)lead poisoningis an example of competitive inhibitor which work at sulfhydryl enzymes (cysteine) ALA dehydratase( found in urine) and ferrochetalase
6) Other example of competitive inhibitors are the Statins(HMG CoA reductase, Methotrexate (inhibits dihydrofolate reductase) interfering with purine the deoxythymidine synthsis thus the Sphase.
7)Allosteric enzyme are also called cooperative enzyme.
The are often regulatory and catalyze an early committed step like PFK-1
in glycolysis. They can have multiple subunits. They can exhibit cooperativity. We already know about the sigmoid and that they can bind at sites other then the active site.
8)At least remember:*****
Competitive---Km increase, --Vmax stays the same
Noncompetitive --noeffect on Km decreases Vmax
Irreversible activators inactivate the enzyme similar to removing the enzyme from the assay, like noncompetitive they have noaffect on Km and decrease Vmax.
Thank Mash for giving the impetus to even talk about this!! :shock:
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