S-sulfenylsulfonate derivative

Conversion to the S-sulfenylsulfonate derivative The high reactivity of sulfhydryl groups imposes serious limitations on attempts to modify selectively other amino acid residues in proteins containing cysteinyl residues. The reversible blocking of free sulfhydryl groups in native proteins with tetrathionate offers one solution to this problem  

An illustration of this approach may be seen in the studies on streptococcal proteinase (Liu 1967). The activity of this enzyme is dependent upon the presence of a free sulfhydryl group. The active form of the enzyme was first converted to the inactive S-sulfenyl-sulfonate derivative. Treatment of this derivative with a chemically-reactive substrate analogue, a-N-bromoacetylarginine methyl ester, resulted in the alkylation of a single histidine residue. The sulfhydryl group of the modified enzyme was regenerated by reduction, however, this did not restore enzymatic activity, thus providing presumptive evidence for the involvement of both a cysteinyl and a histidyl residue in the active site of this enzyme. 

This method of reversible modification of sulfhydryl groups has also 

It should be noted that the formation of a stable sulfenylthiosulfate is a phenomenon observed with native proteins (Pihl and Lange 1962). When simple thiols such as cysteine are reacted with an excess of tetrathionate, S-sulfocysteine is formed (Inglis and Liu 1970). If thiol is in excess, the sulfenylsulfonate can react with a second molecule of thiol to form a disulfide. 

Inglis and Liu (1970) have developed a procedure for the quantitative determination of cystine and cysteine in acid hydrolyzates of proteins, dependent upon the quantitative conversion of cysteinyl residues to S-sulfocysteine, and subsequent quantitation of this derivative by amino acid analysis ( 2.5). 

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