The ATP2A2 (SERCA2) calcium pump is one of several sarcoplasmic and endoplasmic reticulum Ca2+-ATPases responsible for regulating calcium transport across intracellular membranes. Multiple isoforms have been isolated, with ATP2A2a (SERCA2a) found predominantly in the sarcoplasmic reticulum of muscle cells and ATP2A2b (SERCA2b) more ubiquitously expressed in the endoplasmic reticulum of most cell types. An isoform containing a truncated carboxy region (ATP2A2c) is expressed in epithelial and hematopoietic cell lines and may be involved in monocyte differentiation). Post-translational modification of ATP2A2 (SERCA2), including phosphorylation and tyrosine nitration, modify Ca2+ -ATPase activity and calcium transport). Mutation in the corresponding ATP2A2 (SERCA2) gene results in Darier disease, a skin disorder characterized by the presence of dark, keratotic papules or rash found on the head and torso.