The dissociation of b-TSH. The effect of sodium dodecyl sulfate, pH, urea and temperature.

In the present study SDS polyacrylamide gel electrophoresis was used to reinvestigate the conditions under which b-TSH dissociates into its constituent subunits. The effects of SDS, itself, urea, acid pH and temperature were assessed by the decrease in the amount of undissociated TSH and the increase in the dissociated components as revealed by SDS gel electrophoresis. In SDS alone 25--30% dissociation occurred. Pre-treatment with increasing concentrations of urea up to 7.1 M increased the degree of dissociation to 70% after h at room temperature. Maximum dissociation was achieved by treatment at pH 2.5 and 37 degree C for 1 h. In 1 M propionic acid approximately 10% of the TSH was still undissociated after 18 h at 25 degree C.