Purification, some properties and amino acid sequence of Thermus thermophilus HB8 ferredoxin

A stable ferredoxin was purified in a crystalline form from an aerobic, thermophilic bacterium, Thermus thermophilus HB8. The molecular weight of the protein was determined to be 10500 by gel-filtration on Sephadex G-75 and to be 10200 by the sedimentation equilibrium method. The number of iron and acid labile sulfur atoms per mol was determined to be 6.3 and 6.4, respectively. The optical absorption spectrum of the ferredoxin has a broad maximum around 400 nm. The ferredoxin was so thermostable that its absorbance at 400 nm did not decrease after a 45-min incubation at 65 degrees C. The primary structure of the ferredoxin consisting of 78 amino acids was determined by sequence analysis of peptides obtained from a tryptic digest of the S-carboxymethylated ferredoxin and from a Staphylococcus aureus V8 protease digest of the S-aminoethylated derivative. The distribution of cysteine residues and the amino acid sequence around the cysteine residues are very similar to those of Mycobacterium smegmatis ferredoxin.