A New Plant‐Type Ferredoxin from Halobacteria

Abstract

A stable, 2Fe-type ferredoxin has been prepared from Halobacterium halobium and purified by chromatography. A similar ferredoxin was also found in three other Halobacteria. The ferredoxin is present in large amounts—about 1% of the total soluble protein. From amino acid composition a molecular weight of 14800 ± 200 was calculated. The ferredoxin was found to contain two atoms each of iron and sulphide. The midpoint redox potential of the protein is about—345 mV. The electron paramagnetic resonance spectrum of the reduced form shows much similarity to plant and algal ferredoxins with g_x= 1.90, g_y= 1.97 and g_z= 2.07. The same similarity is observed in the optical absorption, optical rotatory dispersion and circular dichroism spectra. However it does not seem to mediate electron transport in the NADP-photoreduction system of chloroplasts. Extracts of the bacterial cells catalyze the reduction of the ferredoxin by NADH.