In order to generate anti-RANK mAb-salmon calcitonin conjugate (mAb-sCT), free thiol groups were generated on our anti-RANK mAb by reacting it in a 10 molar excess of Traut's reagent at room temperature for 1.5 h (Fig. 1a ). Traut's reagent (2-Iminothiolane or 2-IT, Sigma USA), a cyclic thioimidate compound, reacts spontaneously and efficiently with primary amines at pH 7-9 resulting in sulfhydryl addition (17, 18) . No free sulfhydryl moieties were found to be present in our IgG mAb, as determined by Ellman's assay (19) .