Mass spectrometrically derived amino acid sequence of thioredoxin from Chlorobium, an evolutionarily prominent...

The amino acid sequence of the thioredoxin isolated from the photosynthetic green sulfur bacterium Chlorobium thiosulfatophilum was determined chiefly by fast atom bombardment mass spectrometry combined with Edman degradation and tandem mass spectrometry. For this purpose, the protein was digested with trypsin, alpha-chymotrypsin, thermolysin, and Staphylococcus aureus protease or combinations thereof. Chemical cleavage with cyanogen bromide was also used alone or in combination with trypsin. The resulting sequence of 108 amino acids is as follows: Ala-Gly- Lys-Tyr-Phe-Glu-Ala-Thr-Asp-Lys-Asn-Phe-Gln- Thr-Glu-Xle-Xle-Asp-Ser-Asp-Lys-(Ala-Val)-Xle- Val-Asp-Phe-Trp-Ala-Ser-Trp-Cys-Gly-(Pro-Cys)- Met-Met-Xle-Gly-Pro-Val-Xle-Glu-Gln-Xle-Ala-Asp- Asp-Tyr-Glu-Gly-Lys-Ala-Xle-Xle-Ala-Lys-Xle-Asn- Val-Asp-Glu-Asn-Pro-Asn-Xle-Ala-Gly-Gln-Tyr-Gly- Xle-Arg-Ser-Xle-Pro-Thr-Met-Xle-Xle-Xle-Ly s- (Gly-Gly-Lys)-Val-Val-Asp-Gln-Met-Val-Gly-Ala- Xle-Pro-Lys-Asn-Met-Xle-Ala-Lys-Lys-Xle-Asp-Glu-His-Il e-Gly (where Xle represents leucine or isoleucine; sequences in parentheses are based on homology considerations). It exhibits less than 53% homology with Escherichia coli thioredoxin.