Biochemical and EPR characterization of a high potential iron-sulfur protein in Thiobacillus ferrooxidans

A soluble acid-stable high potential iron-sulfur protein (HiPIP) was purified from Thiobacillus ferrooxidans using the periplasmic extraction method. It was isolated in the form of a tetramer consisting of four subunits with a molecular mass of 5582 Da, and its biochemical and biophysical properties were characterized. The N-terminal amino acid sequence (15 residues) was compared with the nucleotide sequence of the iro gene isolated from another strain and the two sequences were found to be identical. The iron content measurement together with optical and EPR spectroscopic studies of the purified protein were consistent with the presence of one [4Fe-4S] cluster per subunit. The EPR spectrum recorded in the oxidized state was attributed to a [4Fe-4S]3+ cluster and the redox potential has been determined to be +380 mV.