Putative heme b importer/sensor involved in heme homeostasis in response to the metabolic state of the cell and to diet. May act as a sensor of cytosolic and/or mitochondrial heme levels to regulate mitochondrial respiration processes, ATP synthesis and thermogenesis. At low heme levels, interacts with components of electron transfer chain (ETC) complexes and ATP2A2, leading to ubiquitin-mediated degradation of ATP2A2 and inhibition of thermogenesis. Upon heme binding, dissociates from ETC complexes to allow switching from mitochondrial ATP synthesis to thermogenesis. Alternatively, in coordination with ATP2A2 may mediate calcium transport and signaling in response to heme.
Subcellular locations: Mitochondrion membrane, Endoplasmic reticulum membrane, Cell membrane
Primarily resides in mitochondria where it interacts with components of the electron transfer chain complexes III, IV and V. Colocalizes with ATP2A2 at the mitochondrial-ER contact junction.
Expressed in non-hematopoietic tissues, with relative abundant expression in brain, placenta, lung, liver and kidney . Also expressed in hematopoietic tissues (fetal liver, spleen, lymph node, thymus, leukocytes and bone marrow) . Found in acidophil cells of the pituitary that secrete growth hormone and prolactin (at protein level) .