The action of urea on the disulphide groups of oxidized glutathione and cystine

Abstract

The kinetics of the reaction between oxidized glutathione and AgNO3 at pH 7-7.6 were studied in the presence of varying concns. of urea. Urea concns. of 4 [image] and above progressively reduced the reaction rate and changed the kinetics towards those characteristic of the cystine-AgNO3 reaction. The rate of the cystine-AgNO3 reaction was slightly reduced by [image] urea, but no further effect was produced by raising the urea concn. to 6 [image]. The character of the kinetics was unchanged. It is suggested that the urea acts by breaking N-H-S bonds between the sulfur and the glutamyl-NH+3 of the oxidized glutathione, thus making it behave like cystine. The existence of this N-H-S bond was discussed in a previous paper. The smaller effect of urea on cystine suggests that this substance normally exhibits some intermolecular N-H-S bonding which hardly influences its chemical behavior.