A four-iron, four-sulfide ferredoxin with high thermostability from Clostridium thermoaceticum

Abstract

A ferredoxin containing only one [Fe4S4] cluster was purified from C. thermoaceticum. It has a molecular weight of about 7,300, a partial specific volume of 0.67, and an isoelectric point of 3.25. Its absorption spectrum has two maxima at 390 nm (ε = 16.8 x 103 M-1 cm-1) and at 280 nm (ε = 24.2 x 103 M-1 cm-1). The absorption at 390 nm is almost half that of other clostridial ferredoxins, which have two [Fe4S4] clusters, and is similar to other ferredoxins with only one [Fe4S4] cluster. The ferredoxin had high thermal stability and retained over 50% of its activity after treatment at 80°C. It functions in the transfer of electrons from pyruvate to nicotinamide adenine dinucleotide phosphate (NADP), which indicates the presence of pyruvate:ferredoxin oxidoreductase and reduced ferredoxin-NADP reductase in C. thermoaceticum. NADPH is used in the synthesis of acetate from CO2 in this organism.