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Author: Subject: Help in Enzymology/curvefitting

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[*] posted on 28-3-2004 at 16:06
Help in Enzymology/curvefitting

hello there!!

I hope someone can help me..
I have left some of my books behind, and I need to write up a report. The only thing, I can't remember how to get Vmax and Km from a recipical graph. If anyone out there can help.. I would appreciate it a lot. I am quite desperate!!

[Edited on 29-3-2004 by chemoleo]
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[*] posted on 29-3-2004 at 07:58

I guess you refer to the LineweaverBurke plot.
1/Vmax equals the intercept of the graph with the vertical axis (reziprocal reaction velocity) and -1/Km equals the intercept with the x-Axis (if defined as reziprocal substrate conzentration).
The formula is 1/v = Km / Vmax x 1/[S] + 1/Vmax.
And you get the graph by measuring V(init.) at different [S].
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Biochemicus Energeticus

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[*] posted on 29-3-2004 at 09:26

Be aware though, that the LB plot is not great for getting accurate values of Vmax/Km - as the reciprocality tends to cluster values, while the line fit does not take this into account.
Better plots are the Ede Hofsteed and Direct Linear Plots.

Better yet, of course, is to perform non-linear regression on the real, unconverted data.
There are freeware programs for this, such as Kaleidagraph, and Sigmaplot (Demo only).
I can't believe they are still teaching this at university, those plots are soo much out of date! Well I guess I suffered the same fate and had to learn them all lol...

Never Stop to Begin, and Never Begin to Stop...
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