Model studies of crotamine self-association

1. The self-association of crotamine in the concentration range from 10 to 40 micrograms/ml was studied at pH 6, 25 degrees C, and at low ionic strength by monitoring the effect of protein concentration on the absorbance at 196 nm. 2. Of the several mathematical models tested, an equilibrium between monomers and trimers with an association constant of 1.50 x 10(11) M-2 gives an adequate representation of the phenomenon. However, a non-ideal, two-stage model describing an equilibrium among monomers, dimers, and trimers gives the best fit of the experimental data. 3. The equilibrium constants found for dimerization and trimerization were 1.70 x 10(3) M-1 and 3.37 x 10(6) M-1, respectively. 4. This model was confirmed by polyacrylamide gel electrophoresis where a trimer band was separated from an interconverting monomer-dimer band.