1 Iron—Sulfur Proteins

Abstract

This chapter discusses iron-sulfur proteins. Iron proteins are divided into three groups. If the iron atom is coordinated to a porphyrin, the protein is called a “hemoprotein,” irrespective of the chemistry of the axial ligands. If the iron is coordinated to sulfur from either cysteine or from inorganic sulfur, then the protein is called an “iron-sulfur protein.” Any iron protein, which does not belong in either of these two categories, is disposed of as “other.” Iron-sulfur proteins are divided into four categories: (1) ferredoxin, (2) high potential iron-sulfur proteins, (3) rubredoxins, and (4) conjugated iron-sulfur proteins. Ferredoxin comprises those iron-sulfur proteins with an equal number of iron and labile sulfur atoms, and a negative midpoint redox potential at pH 7. Rubredoxins comprises those iron-sulfur proteins without acid-labile sulfur characterized by having iron in a typical mercaptide coordination, that is, one center surrounded by four cysteine or equivalent sulfur ligands. Conjugated iron-sulfur proteins comprise those proteins containing iron and labile sulfur or iron in a typical mercaptide coordination, but also containing additional prosthetic groups. The simplest iron-sulfur protein is typified by the rubredoxin from clostridium pasteurianum.