Studies on the Structure of T4 Thioredoxin

An improved purification method for the preparation of thioredoxin from phage T4-infected Escherichia coli cells is described. Homogeneous T4 thioredoxin contained 87 amino acid residues. From a tryptic digest of reduced and carboxymethylated T4 thioredoxin 12 peptides were isolated by paper electrophoresis and chromatography. Amino acid sequence determinations by enzymatic fragmentation and 5-dimethylaminonaphthalene-1-sulfonyl-Edman degradation showed that 11 of the tryptic peptides accounted for the total amino acid composition of T4 thioredoxin. The 12th tryptic peptide resulted from incomplete tryptic digestion of a Lys-Arg peptide bond.