Sulfhydryl Groups in Human Ceruloplasmin

Sulfhydryl groups in human ceruloplasmin were determined with β‐hydroxyethyl‐2,4‐dinitrophenyl disulfide. In the native ceruloplasmin one sulfhydryl group has been found. In Urea solutions the number of sulfhydryl groups titrated was found to depend on the concentration of urea and on the presence of EDTA. Two sulfhydryl groups were unmasked in 7 M urea alone, and a third after addition of EDTA. The unmasking of sulfhydryl groups in urea was coincident with the bleaching of ceruloplasmin and with the loss of its oxidase activity.