ACONITASE - AN IRON-SULFUR ENZYME

This chapter describes an iron–sulfur enzyme—aconitase. Although the presence and function of the Krebs cycle enzyme aconitase has been known for over 50 years, it is only recently that many of the unusual properties of this protein can be understood in molecular terms. Through the application of spectroscopy, especially Mössbauer (MB) spectroscopy in combination with electron paramagnetic resonance (EPR), in addition to chemical methods, it was established that the activation process involved the conversion of a [3Fe–4S] cluster to a [4Fe–4S] form. These earlier studies demonstrated that the iron added during this reaction, labeled Fea, was site specific. These discoveries in the early 1980s allowed for the subsequent design of a number of experiments to investigate the details of the role of the cluster in the catalytic mechanism of the enzyme. Aconitase and ferredoxin (Fd) II of Desulfovibrio gigas (D. gigas) were among the first proteins that were shown to contain a 3Fe cluster. Because of its low molecular mass and its stability, Fd II of D. gigas became the prime example for spectroscopic characterization of proteins containing 3Fe clusters. © 1992 Academic Press, Inc.