A recently proposed semi-empirical method for calculating binding free
energies was used to examine the binding of a variety of substrates t
o cytochrome P450cam, For a set of 11 different potential substrates o
f cytochrome P450cam, both the absolute and relative binding free ener
gies were generally well reproduced. The mean error in the calculated
absolute binding free energy for all 11 compounds is 0.55 kcal/mol. Fo
rty-eight out of 55 calculated relative binding free energies have the
correct sign and the mean unsigned error between calculated and exper
imental relative binding free energies is 0.77 kcal/mol, For one subst
rate, thiocamphor, the effect of substrate orientation on the calculat
ed binding free energy was examined, The ability of this method to pre
dict the effect of active site mutations was also examined in two case
s.