Purification and biochemical characterization of an organic-solvent-tolerant thioredoxin from dromedary pancreas

We purified to homogeneity and characterized a heat stable thioredoxin which catalyzes thiol/disulfide exchange reaction, for the first time from dromedary pancreas. The purification involved heat and acidic treatment (90 °C; pH 2.5), precipitation by ammonium sulphate and ethanol, respectively followed by sequential column chromatography reverse HPLC column, and it resulted in an apparently pure protein after a 217-fold purification with a final yield of 55% of the initial thioredoxin activity. The thioredoxin preparation obtained was homogeneous as judged by polyacrylamide gel electrophoresis and the presence of valine as the only NHt-terminal amino acid. MALDI-TOF mass spectrometry revealed that the protein has a molecular mass of 11,302.9 Da. The first 40 amino-acid residues at the N-terminal extremity of purified DrTrx was determined by automatic Edman degradation and showed a high sequence homology with known Thioredoxin. It contained he tetrapeptide-Cys-Gly-Pro-Cys-, which constitutes the active site of mammalian thioredoxins. DrTrx activity was compatible with the presence of organic solvents and the maximum activity appeared at pH 7.5 using the insulin precipitation assay. Thioredoxin stability in the presence of organic solvents, as well as in acidic and alkaline pHs and at high temperatures makes it a good candidate for its application in pharmaceutical and food industry.