MAGNETIC CIRCULAR-DICHROISM STUDY OF THE SELENIUM-SUBSTITUTED FORM (FE FE3SE4) OF BOVINE HEART ACONITASE

The selenium-substituted inactive form of mitochondrial aconitase cont ains one [3Fe-4Se](1+/0) cluster [Surerus, Kennedy, Beinert and Munck (1989) Proc. Natl. Acad. Sci, U.S.A. 87, 9846-9850]. This cluster was studied in both oxidized and reduced states by magnetic CD (MCD) and E PR spectroscopy. In the MCD spectra, intensity and transition waveleng th shifts are observed when compared with the spectra of the native [3 Fe-4S](1+0) cluster. These changes are used to differentiate between t he charge transfer transitions originating from inorganic and cysteiny l sulphur. Using also the data from the EPR spectra, the spin ground s tate is assigned as S = 1/2 for the oxidized [3Fe-4Se](1+) cluster and S = 2 for the reduced [3Fe-4Se](0) cluster.