[R] Michaelis-menten equation

[Peter Dalgaard]

"Chun-Ying Lee" <u9370004 at cc.kmu.edu.tw> writes:

> 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,


Check your simulation. There is no way that curve is consistent with
Km in the middle of the y range!

> ---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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-- 
   O__  ---- Peter Dalgaard             Øster Farimagsgade 5, Entr.B
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