Need help with NonlinearFit

*To*: mathgroup at christensen.cybernetics.net*Subject*: [mg1872] Need help with NonlinearFit*From*: "Timothy W. Weber" <tww5y at kelvin.seas.virginia.edu>*Date*: Wed, 9 Aug 1995 22:40:04 -0400*Organization*: uva

I'm trying to fit two sets of kinetic data using NonlinearFit and I'm having a lot of difficulty doing so. My reaction is bisubstrate, S1 and S2, let's say. My rate expression is r = a S1 S2/(b + S1 (c + S2)) where a, b and c are my kinetic constants. My problem is that one set of data is for varying S1 at constant S2, while the other is for varying S2 at constant S1. There is one crossover point, which unfortunately didn't have the exact same value in both studies. What's happening is that I'm getting two sets of kinetic parameters for the two different sets of data, and theoretically, they should be capable to fitting to only set of parameters, right? Any suggestions? My next step is to average the values for the crossover point and replace the individual values with the average. Yes? No? I'm in a real quandry and under somewhat of a time constraint since these are for my dissertation, which is coming up in a few short weeks. Any help would be appreciated. Thanks in advance. Tim -- Tim Weber Graduate Student, Chemical Engineering