"In addition to the dithiolene sulfurs of the pterin moiety and two oxo groups, the molybdenum atom of Moco needs the addition of a terminal inorganic sulfur to provide enzyme activity to these enzymes (55). This final step is catalyzed by the Moco sulfurase protein (ABA3 in plants and HMCS in humans) " [PMID:23539623]. HMCS is an alternative name for MOCOS (in UniProt, https://www.uniprot.org/uniprotkb/Q96EN8/entry)