The sulfhydryls of avian ovalbumins, bovine β-loctoglobulin, and bovine serum albumin

Abstract

The sulfhydryl groups in chicken ovalbumin, bovine β-lactoglobulin, and bovine serum albumin were studied with four different types of chemical reagents: p-chloromercuribenzoate, iodine, N-ethylmaleimide and 5,5′-dithiobis (2-nitrobenzoic acid). Native chicken ovalbumin had three weakly reactive (“masked”) SH groups, and after denaturation it had four reactive groups. Native β-lactoglobulin had no, or only very weakly, reactive groups; after denaturation it had two reactive groups. Serum albumin gave similar values before and after denaturation, but the values of different preparations varied between 0.3 and 0.75 SH groups. In comparative analyses of the SH contents of the egg whites of 22 different avian species, only one other bird besides the domestic chicken showed additional SH groups after denaturation. This bird was the red jungle fowl, which is very closely related to the domestic chicken. The 5,5′-dithiobis (2-nitrobenzoic acid) was considered the most useful reagent for routine determinations of the approximate total content of SH groups.