The V1 domain of V-ATPases is a peripheral membrane domain composed of eight different subunits (A-H) that are expressed as multiple isoforms in a tissue-specific manner. The V1 domain is responsible for ATP hydrolysis. The non-catalytic V1 subunits do not hydrolyze ATP directly but provide regulatory functions and/or interact with the V0 domain. (Adapted from PMID:20450191 and FBrf0188241).