Re: [R] Michaelis-menten equation

From: Chun-Ying Lee <u9370004_at_cc.kmu.edu.tw>
Date: Wed 20 Jul 2005 - 12:26:25 EST

Hi,

   We used known Vm and Km to simulate the data set (time, Cp) without adding random error in there. Yes, the line looks like very close to a straight line. But why can't we obtain the correct values with fitting process? We used optim first and then followed by using nls to fit the model. Thanks.

regards,
---Chun-ying Lee
>
> Hmm, sorry, no. I'm talking through a hole in my head there.
>
> Vm*y/(Km+y) makes OK sense. Vm is what you get for large y - passing
> from 1st order to 0th order kinetics. However, looking at the data
>
> plot(PKindex)
> abline(lm(conc~time,data=PKindex))
>
> shows that they are pretty much on a straight line, i.e. you are
> in the domain of 0-order kinetics. So why are you expecting the rate
> of decrease to have changed by roughly 3/4 (from 2/3*Vm/Vd at y=2*Km
> to 1/2*Vm/Vd at y=Km when you reach 4.67)??
>



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