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 p urified from Thiobacillus ferrooxidans using the periplasmic extractio n 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 bi ophysical properties were characterized. The N-terminal amino acid seq uence (15 residues) was compared with the nucleotide sequence of the i ro gene isolated from another strain and the two sequences were found to be identical. The iron content measurement together with optical an d EPR spectroscopic studies of the purified protein were consistent wi th the presence of one [4Fe-4S] cluster per subunit. The EPR spectrum recorded in the oxidized state was attributed to a [4Fe-4S](3+) cluste r and the redox potential has been determined to be + 380 mV.