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

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Abstract
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.