Anti-NAC antibodies are protein reagents that detect specific antigens. The NAC antigen is another term for the human protein X-linked Kx blood group antigen, Kell and VPS13A binding protein, encoded by the XK gene. The protein is known to function in the regulation of intracellular calcium, among other biological roles. Canonically, it has an amino acid length of 444 residues and a mass of 50.9 kilodaltons. Its subcellular localization is in the ER and it is notably expressed in skeletal muscle, heart, brain, and pancreas; low levels in the placenta, lung, liver, and kidney. The NAC protein is a member of the XK protein family.