The function of ENSG00000119686 (FLVCR2, FLVCR choline and putative heme transporter 2) is as follows. Choline uniporter that specifically mediates choline uptake at the blood-brain-barrier (PubMed:38302740, PubMed:38778100, PubMed:40972734). Responsible for the majority of choline uptake across the blood-brain-barrier from the circulation into the brain (By similarity). Choline, a nutrient critical for brain development, is a precursor of phosphatidylcholine, as well as betaine (By similarity). Also mediates transport of ethanolamine (PubMed:38778100). Choline and ethanolamine transport is not coupled with proton transport and is exclusively driven by the choline gradient across the plasma membrane (PubMed:38778100). However, the presence of an inwardly directed proton gradient enhances choline uptake (By similarity). Also acts as a heme b transporter (PubMed:20823265, PubMed:32973183). Required to regulate mitochondrial respiration processes, ATP synthesis and thermogenesis (PubMed:32973183). 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 (PubMed:32973183). Upon heme binding, dissociates from ETC complexes to allow switching from mitochondrial ATP synthesis to thermogenesis (PubMed:32973183). {ECO:0000250|UniProtKB:Q91X85, ECO:0000269|PubMed:20823265, ECO:0000269|PubMed:32973183, ECO:0000269|PubMed:38302740, ECO:0000269|PubMed:38778100}.