Copper ion transmembrane transporter involved in the export of copper out of the cells, such as the efflux of hepatic copper into the bile. ATP + Cu(+)(in) + H2O = ADP + Cu(+)(out) + H(+) + phosphate Monomer. Interacts with COMMD1/MURR1 (By similarity). Interacts with DCTN4, in a copper-dependent manner (By similarity). Interacts with ATOX1 (By similarity). Interacts (via C-terminus) with ZBTB16/PLZF (By similarity). Predominantly found in the trans-Golgi network (TGN). Not redistributed to the plasma membrane in response to elevated copper levels. Expressed in brain, liver, kidney, spleen and stomach. In brain, detected in neuronal cells of the hippocampal formation, olfactory bulbs, cerebellum, cerebral cortex and nuclei in the brainstem. Isoform PINA is expressed during night in adult pineal gland (pinealocytes) and retina. Isoform PINA is not detected in other tissue. Isoform PINA is expressed during daytime in embryonic pineal (postnatal day 2 and 7) and embryonic retinal pigment epithelium (embryonic day 14.5 and postnatal day 16). Daytime expression disappears in pineal at postnatal day 16 and in adult retina. Each HMA domain can bind a copper ion, they are tightly packed and closely interact with each other. Wild-type ATP7B can usually be loaded with an average 5.5 copper atoms per molecule (By similarity). Deficiency of Atp7b expression is the cause of the Long-Evans Cinnamon (LEC) phenotype, inherited in an autosomal recessive manner, characterized by excessive hepatic copper accumulation, defective holoceruloplasmin biosynthesis, impaired biliary copper excretion and the development of necrotizing hepatitis by 4 months of age. Produced by alternative splicing. Does not show copper transport activity. Produced by alternative initiation at Met-815 of isoform Long. Shows copper transport activity. Belongs to the cation transport ATPase (P-type) (TC 3.A.3) family. Type IB subfamily.