57. Which of the following protein modifying reagents is correctly defined?
(A) 2-mercaptoethanol: readily oxidizes -SH group and forms disulfidebridges in proteins.
(B) cyanogen bromide: the Br ion reacts with the nucleophilic sulfur atom of thetarget amino acid that leads to protein cleavage.
(C) phenylisothiocyanate: reacts with free carboxyl groups in protein.
(D) cyanogen bromide: specifically reacts with internal cysteine residues
(E) guanidinium HCl: disrupts ionic interactions and hydrogen bonds