Studies on self association of proteins. The self association of alpha-chymotrypsin at pH 8.3 and ionic strength 0.05.

The self-association of a-chymotrypsin at pH 8.3
and p = 0.05 was studied by measuring the weight-average
molecular weight by the Archibald method and the sedimentation
coefficient as a function of protein concentration. Considerable
autolysis of the protein occurred under the experimental
conditions used. A method was devised to measure the
extent of autolysis.,The molecular weight data were corrected
for the presence of the autolysis product(s) which itself did
not undergo self-association. An analysis of the experimental
molecular weight data for various models of self-association showed that indefinite self-association model with nonideality
term set to zero fitted the data the best. However, analysis of
the sedimentation coefficient data showed that a monomerhexamer
equilibrium, without any intermediate species,
fitted the data the best. Pressure in sedimentation velocity
experiments did not affect SPO,., values but affected the shape
of the velocity patterns. The addition of autolysis product(s) of
the enzyme did not affect self-association as revealed by
molecular weight data, but affected the sedimentation velocity
patterns.