An iron-sulfur protein without acid-labile sulfur, in which an iron centre is coordinated by four sulfur-containing ligands, usually cysteine. The function, where known, is an electron carrier.
Source:
PAC, 1997, 69, 1251. 'Glossary of terms used in bioinorganic chemistry (IUPAC Recommendations 1997)' on page 1296 (https://doi.org/10.1351/pac199769061251)