P4-ATPase flippase which catalyzes the hydrolysis of ATP coupled to the transport of aminophospholipids from the outer to the inner leaflet of various membranes and ensures the maintenance of asymmetric distribution of phospholipids. Phospholipid translocation seems also to be implicated in vesicle formation and in uptake of lipid signaling molecules. May be responsible for the maintenance of asymmetric distribution of phosphatidylserine (PS) in spermatozoa membranes. Involved in acrosome reactions and binding of spermatozoa to zona pellucida. ATP + H2O + phospholipidSide 1 = ADP + phosphate + phospholipidSide 2. a 1,2-diacyl-sn-glycero-3-phospho-L-serine(out) + ATP + H2O = a 1,2-diacyl-sn-glycero-3-phospho-L-serine(in) + ADP + H(+) + phosphate Isoform 3 was only detected in testis. Association with flippase complex beta subunits TMEM30A and TMEM30A has not been detected, neither did their coexpression change the localization in ER. Belongs to the cation transport ATPase (P-type) (TC 3.A.3) family. Type IV subfamily.