Arsenate-mycothiol transferase (, ArsC1, ArsC2, mycothiol:arsenate transferase) is an enzyme with systematic name mycothiol:arsenate S-arsenotransferase. This enzyme catalyses the following chemical reaction
<div align=center><small>mycothiol + arsenate arseno-mycothiol + H<sub>2</sub>O</small></div>
Reduction of arsenate is part of a defence mechanism of the cell against toxic arsenate.