Separation of glutathione and its related amino acids by nanofiltration

Abstract

Nanofiltration experiments of glutathione and its related amino acids ( l-glutamate, l-cysteine, glycine, and l-glutamine) were carried out using NTR-7450 nanofiltration membrane in order to determine the potential use of nanofiltration in the enzymatic glutathione synthesis, in which the reaction equilibria are need to be driven to production by separating glutathione from starting substrates. In the experiments with a single component system, the rejection of NTR-7450 membrane for the electrolytes corresponded well to the ratio of their anionic species varying with pH. Difference in the rejection between glutathione and some amino acids was maximal in the neutral pH region: at pH 7.4, the rejection for glutathione and l-glutamate was almost 100%, whereas that for l-cysteine, glycine, and l-glutamine was below 30%. In the presence of divalent metal ions, the rejection for glutathione and l-glutamate decreased with increasing the metal concentration, probably due to partial neutralization of negative charges of the electrolytes forming complexes with the metal ions. In the experiments with a multi-component system, glutathione was completely blocked again by the membrane in a range of glutathione concentration from 0.1 to 5.0 mM in the presence of 1.0, 2.0, or 5.0 mM each of l-glutamine, glycine, and l-cysteine. The amino acid rejection decreased with increasing the amino acid concentrations. These results suggest that nanofiltration would be applicable to the separation of glutathione from substrates, l-cysteine, glycine, and l-glutamine, in the enzymatic glutathione synthesis.