Kinetic and spectrophotometric studies of binding of iron(III) by glutathione

Abstract

. Can. 9. Chem. 54, 3192 (1976).In this report, determination of unbound aquo iron species is accomplished by a kirretic n~et/7oc/involving reaction with sulfosalicylic acid (SSA) on a time ssale which is very short with respect to reaction of SSA with the glutathione complexes of iron. The data are used to calculate conditional binding constants for Fe(lI1) to glutathione. Binding constants in 0.1 M ionic strength media were obtained between p H 1 and 2.4 by the kinetic method. and near p H = 3 by spectrophotometry arrd by examillation of the ratio of rate of complex formation and dissociation. The conditional binding 'constant' betweetz p H 1 and 3 is represented as pK = -1.96 -O.5OpH. This is consistent with the importance of reactions involving only very limited proton release. Spectrophotometric data show that the -OH group on Fe(OH)*-is lost on glutathione complexing. Kinetics of the complex formation reaction between aquo iron(I1I) species and glutathione are slower than rates of reaction of iron (111) with simple ligands.The glutathione system is regarded as a model system important to natural water chemistry because it is a widely distributed biological sulfur-containing chelating agent. Des donnkes spectrophotomCtriques demontrent que le groupe OH du Fe(OH)2+ est perdu lors de la complexation avec du glutathion. La cinktique de la reaction de formation du complexe entre les espkces aquo-ferriques et le glutathion sont plus faibles que les vitesses de rkaction du fer(II1) avec des ligands simples.On considkre que le systkme de glutathion est un systkme n~odkle important pour la chinlie de l'eau naturelle parce que c'est un agent biologique chelata~~t contenant du soufre qui est distribui trks largement.[Traduit par le journal]