The Isolation and Primary Structure of a Peptide Containing the Oxidation-Reduction Active Cystine of Escherichia coli Thioredoxin Reductase

An octapeptide from Escherichia coli thioredoxin reductase has been isolated and sequenced; it contains the cystine previously shown to take part in electron transfer. The peptide was isolated from a peptic digest of a derivative in which the free sulfhydryls of the enzyme had been reacted with the colored maleimide, N-(4-dimethylamino-3,5-dinitrophenyl)maleimide. The sequence of this peptide as determined by subtractive Edman degradation was: [see PDF for sequence] The minimum molecular weight based on amino acid analysis and flavin content has been redetermined on highly purified enzyme to be 36,500 per FAD or 73,000 per mole of enzyme. The total half-cystine content was found to be five per FAD, indicating three cysteines and one cystine per FAD.