Iron sulfur proteins of the purple sulfur bacterium Ectothiorhodospira shaposhnikovii

Abstract

In addition to several cytochromes three iron sulfur proteins were detected in mixotrophically grown cells of Ectothiorhodospira shaposhnikovii, a member of the Chromatiaceae. They were identified as a bacterial ferredoxin and two high potential iron sulfur proteins (HIPIPs). The two HIPIPs were purified and characterized. They were named according to their differing retention times on a DEAE-cellulose column using a continuous NaCl gradient: “early” and “late” HIPIP. The HIPIPs contain 4 mol of non-heme iron and 4 mol of acid labile sulfur per mol protein. Under the conditions of purification the “early” HIPIP (E _{m, 7}+270 mV) was present in a semi-reduced state. Using ion-exchange chromatography the “early” HIPIP could be split into a reduced green-brown (pI=3.7) and an oxidized red-brown (pI=3.9) fraction. The “late” HIPIP (pI=3.8) showed a midpoint potential of only+155 mV, the lowest redox potential of a HIPIP described so far.