The enzyme transfers sulfur to form a thiocarboxylate moiety on the C-terminal glycine of the small subunit of EC?2.8.1.12, molybdopterin synthase. In the human, the reaction is catalysed by the rhodanese-like C-terminal domain (cf. EC?2.8.1.1) of the MOCS3 protein, a bifunctional protein that also contains EC?2.7.7.80, molybdopterin-synthase adenylyltransferase, at the N-terminal domain.
