Evidence for the co-existence of glutathione reductase and trypanothione reductase in the non-trypanosomatid Euglenozoa: Euglena gracilis Z

Two NADPH-dependent disulfide reductases, glutathione reductase and trypanothione reductase, were shown to be present in Euglena gracilis, purified to homogeneity and characterized. The glutathione reductase ( M r 50 kDa) displays a high specificity towards glutathione disulfide with a K M of 54 μM. The amino acid sequences of two peptides derived from the trypanothione reductase ( M r 54 kDa) show a high level of identity (81% and 64%) with sequences of trypanothione reductases from trypanosomatids. The trypanothione reductase is able to efficiently reduce trypanothione disulfide ( K M 30.5 μM) and glutathionylspermidine disulfide ( K M 90.6 μM) but not glutathione disulfide, nor Escherichia coli thioredoxin disulfide, nor 5,5′-dithiobis(2-nitrobenzoate) (DTNB). These results demonstrate for the first time (i) the existence of trypanothione reductase in a non-trypanosomatid organism and (ii) the co-existence of trypanothione reductase and glutathione reductase in E. gracilis.