Catalytic component of a P4-ATPase flippase complex which catalyzes the hydrolysis of ATP coupled to the transport of phospholipids, in particular phosphatidylcholines (PC), from the outer to the inner leaflet of the plasma membrane (By similarity). May participate in the establishment of the canalicular membrane integrity by ensuring asymmetric distribution of phospholipids in the canicular membrane (PubMed:21820390). Thus may have a role in the regulation of bile acids transport into the canaliculus, uptake of bile acids from intestinal contents into intestinal mucosa or both and protect hepatocytes from bile salts (PubMed:14976163, PubMed:21820390, PubMed:20126555). Involved in the microvillus formation in polarized epithelial cells; the function seems to be independent from its flippase activity (By similarity). Participates in correct apical membrane localization of CDC42, CFTR and SLC10A2 (PubMed:26416959). Enables CDC42 clustering at the apical membrane during enterocyte polarization through the interaction between CDC42 polybasic region and negatively charged membrane lipids provided by ATP8B1 (PubMed:26416959). Together with TMEM30A is involved in uptake of the synthetic drug alkylphospholipid perifosine (By similarity). Required for the preservation of cochlear hair cells in the inner ear (PubMed:19478059). According PubMed:20852622 is proposed to act as cardiolipin transporter during inflammatory injury; the function is questioned by PubMed:21475228 (PubMed:20852622, PubMed:21475228). ATP + H2O + phospholipidSide 1 = ADP + phosphate + phospholipidSide 2. a 1,2-diacyl-sn-glycero-3-phosphocholine(out) + ATP + H2O = a 1,2-diacyl-sn-glycero-3-phosphocholine(in) + ADP + H(+) + phosphate 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 Component of a P4-ATPase flippase complex which consists of a catalytic alpha subunit ATP8B1 and an accessory beta subunit TMEM30A (PubMed:30018401). The flippase ATP8B1:TMEM30A complex can form an intermediate phosphoenzyme in vitro. Also interacts with beta subunit TMEM30B. Exit from the endoplasmic reticulum requires the presence of TMEM30A or TMEM30B. Localizes to apical membranes in epithelial cells. Hepatocytes, bile duct, intestinal epithelial cells (cholangiocytes and ileocytes), and pancreatic acinar cells. Mice have unimpaired bile secretion, and no liver damage, but show mild abnormalities including depressed weight at weaning and elevated serum bile salt levels. Do not suffer from jaundice or diarrhea and have normal serum bilirubin levels and normal liver enzyme activities, except for mildly elevated serum AST (aspartate aminotransferase) activity. Display unimpaired transhepatic bile salt transport and are resistant to bile salt-induced cholestasis. Upon bile salt feeding, demonstrate serum bile salt accumulation, hepatic injury and expansion of the systemic bile salt pool and this failure of bile salt homeostasis occurs in the absence of any defect in hepatic bile secretion (PubMed:14976163). Mutant mice with B6 background show greater abnormalities than 129 and/or F1 background ones. Pups of B6 background gain less weight. In adult B6 background has lower serum cholesterol levels, higher serum alkaline phosphatase levels, and larger livers. After challenge with cholate-supplemented diet, these mice exhibit higher serum alkaline phosphatase and bilirubin levels, greater weight loss and larger livers (PubMed:20126555). Belongs to the cation transport ATPase (P-type) (TC 3.A.3) family. Type IV subfamily.