The effect of sulphydryl reagents on the human thyroid microsomal antigen.

High sensitivity of the microsomal antigen epitopes recognized by autoantibodies in sera of patients with thyroid autoimmune diseases to disulphide bridge reducing agents have been detected. The shape of the inactivation curve is different for sera obtained from different patients, but for most sera 50% inactivation is obtained below 1 mM of dithioerythritol. The inactivation strongly depends on the pH of the incubation buffer and is most pronounced at alkaline pH (9.6). Cross-linking of the soluble microsomal antigen by glutaraldehyde makes the epitopes resistant to DTE. Binding of the microsomal antigen to polystyrene makes it up to 5 times more resistant to DTE. The microsomal peroxidase enzymatic activity is destroyed by low concentration of dithioerythritol and the inactivation is not dependent on the buffer pH (7.4-9.6). The data demonstrated that the major microsomal antigen epitope is discontinuous (conformation dependent).