Thioredoxin 2: Cleavage with Cyanogen Bromide

A simple and highly reproducible method for the preparation of thioredoxin from Escherichia coli B was worked out.On treatment with cyanogen bromide thioredoxin was cleaved into two peptides which were separated by chromatography on Sephadex G‐50. The smaller peptide (peptide B) contained 37 amino acids and represented the N‐terminal fragment of thioredoxin, while the larger peptide (peptide A) contained the remaining 71 or 72 C‐terminal amino acids. The cystine and tryptophan residues of thioredoxin were found in peptide B.Both peptides were characterized with respect to amino acid composition and were studied by spectrofluorimetry. The increase in quantum yield of the tryptophan emission resulting from the reduction of the disulfide bridge of peptide B was considerably smaller than the corresponding increase resulting from the reduction of the disulfide bridge of thioredoxin [1].Peptide B was not reduced by TPNH and thioredoxin reductase and showed no activity in the reduction of cytidine diphosphate with ribonucleoside diphosphate reductase from Escherichia coli.