The aconitase of yeast. IV. Studies on iron and sulfur in yeast aconitase.

Chemical analyses were carried out to determine the active components of the crystalline aconitase [EC 4.2.1.3] of Candida lipolytica. The enzyme contained 2 atoms of non-heme iron, 1 atom of labile sulfur, and 6 sulfhydryl groups per molecule. One atom of the non-heme iron was released by the addition of metal-chelating agents such as sodium citrate, sodium nitrilotriacetate (NTA) or sodium ethylenediaminetetraacetate (EDTA) without loss of the enzyme activity. The non-heme iron and labile sulfur were released by the addition of sulfhydryl reagents such as rho-chloromercuribenzoate (PCMB), sodium mersalyl or urea with loss of the enzyme activity. o-Phenanthroline reacted with the iron atoms in the enzyme at pH 6.0 with loss of the activity. These results show that yeast aconitase is an iron-sulfur protein and that only one of the two non-heme iron atoms is essential for enzyme activity.