Yeast Thioredoxin

Abstract

Reduced and carboxymethylated thioredoxin II from Saccharomyces cerevisiae was digested with trypsin and cleaved with cyanogen bromide in separate experiments. From the amino‐acid sequences of isolated peptides after chymotryptic or peptic hydrolysis an alignment of a 17‐residue sequence around the redox‐active disulfide of thioredoxin II was possible as follows: . Comparison of this structure with the corresponding amino‐acid sequence of the thioredoxin from Escherichia coli B showed identical residues in 10 consecutive positions which included the tryptophan residue, the disulfide ring and the five residues following this on the COOH‐terminal side. The COOH‐terminal sequence of yeast thioredoxin II was: ‐Glu‐Ala‐Ile‐Ala‐Ser‐Asn‐Val and the NH 2 ‐terminal residue was valine. The sequence results indicated a considerable homology in primary structure between yeast and E. coli thioredoxins and suggested the existence of a common ancestral gene for thioredoxins. The sequence of a peptide from the active site of yeast thioredoxin I showed that the structure around the disulfide bridge was: . This indicated that thioredoxin I and II from yeast have different primary structures.