Cleavage of the SS bond in 5,5′-dithiobis-(2-nitrobenzoic acid) in the presence of a cationic detergent An approach to the cleavage of the SS bond in bovine plasma albumin

Abstract

The hydrolysis of 5,5′-dithiobis-(2-nitrobenzoic acid) was studied at pH 9.20 and 25°C in presence of tetradecyltrimethylammonium bromide or micellar tetradecyltrimethylammonium bromide. The reaction was pseudo-unimolecular reaction with regard to the concentration of dithionitrobenzoic acid. The rate constant k 1 depended on the tetradecyltrimethylammonium bromide concentration and on the ionic strength of the buffer solution. At a constant ionic strength, the value of k 1 increased with the increase in the tetradecyltrimethylammonium bromide concentration, attained maximum at a certain concentration above the critical micelle concentration, and then decreased. The value of k 1 was larger when the ionic strength was lower. The rate of hydrolysis at the ionic strength 0.1 was the same as that without tetradecyltrimethylammonium bromide. On the contrary, sodium dodecyl sulfate or micellar sodium dodecyl sulfate had no effect on the rate of hydrolysis. These results lead to the conclusion that the SS bond is cleaved easier, when it is surrounded by the cationic detergent. The SH/S-S exchange reaction of bovine plasma albumin in the presence of cationic detergent was slower when the ionic strength was higher. The fact could be explained by assuming that the exposed SS bond is surrounded by the cationic detergent. Further, it was speculated that some SS bonds in albumin are surrounded by the positively charged basic amino acid residues.