I need to choose a non linear regression model for, protein phosphorylation over time response, not like enzyme kinetics, for this kind of data

The michaelis menten model does not behave properly, becouse, I am not dealing with a susbtrate concentration, instead I got a signal response, for receptor stimulation.
So, please help me to get a working model for a non linear regression of this kind.
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Edited by Felipillo, 17 May 2012 - 10:03 AM.















