The Aconitase of Yeast. IV. Studies on Iron and Sulfur in Yeast Aconitase1

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Abstract
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 ethylenedi-aminetetraacetate (EDTA) without loss of the enzyme activity. The non-heme iron, and labile sulfur were released by the addition of sulfhydryl reagents such as p-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.

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