The C chain is a proteolipid, and one of the membranous subunits of the nonenzymatic component of the Sul-ATPase complex. Sul-ATPase is composed of six (or maybe five) subunits: alpha, beta, delta, gamma, C (proteolipid), and possibly epsilon. Belongs to the V-ATPase proteolipid subunit family. Was originally reported as originating from S.acidocaldarius.