An @IT06780@ without @AT06794@, in which an iron centre is @C01329@ by four sulfur-containing @L03518@, usually cysteine. The function, where known, is an electron @C00859@.
Source: PAC, 1997, 69, 1251. (Glossary of terms used in bioinorganic chemistry (IUPAC Recommendations 1997)) on page 1296 [Terms] [Paper]