[R] Michaelis-menten equation

Chun-Ying Lee u9370004 at cc.kmu.edu.tw
Wed Jul 20 04:26:25 CEST 2005


   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.

---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)??

More information about the R-help mailing list