[RASMB] Program to fit data to heteroassociation

[petoh]

Hi
Sorry if this is a trivial question.
I am investigating whether two proteins interact and if so, what is their
dissociation constant.  Based upon the Review by Laue and Stafford, I have
derived an equation to fit the data to, in the first instance.  However I,
do not know how to tell Nonlin to fit the data to this equation, or if there
is any other program I can fit the data to a user defined equation.

Does anyone have any suggestions?
Nonlin versions are for Mac or PC.  I do not have access to Vax-VMS.

Many thanks for your help

Heather Peto