Availability of protein amino groups in senile nuclear cataract.

The reagent 2, 4, 6-trinitrobenzenesulfonic acid was used to probe the status of protein amino groups in the nuclei of control (cortical cataract) and advanced senile nuclear cataractous lenses. There was no significant difference in the content of reactive amino groups in control and senile nuclear cataractous lenses. The great majority, if not all, of the epsilon-amino groups of lysine residues in lens protein exist in the free form. There was no detectable difference in the protein sulfhydryl content of control and advanced senile nuclear cataractous lens proteins after reduction with mercaptoethanol.