Olfactory receptor (PubMed:29249973, PubMed:27226631). Activated by the odorant, beta-ionone, a synthetic terpenoid (PubMed:29249973, PubMed:27226631, PubMed:19389702). The activity of this receptor is probably mediated by G-proteins leading to the elevation of intracellular Ca(2+), cAMP and activation of the protein kinases PKA and MAPK3/MAPK1 (PubMed:27226631, PubMed:29249973). Stimulation of OR51E2 by beta-ionone affects melanocyte proliferation, differentiation, and melanogenesis (PubMed:27226631). Activation of OR51E2 by beta-ionone increases proliferation and migration of primary retinal pigment epithelial (RPE) cells (PubMed:29249973). Activated also by the short-chain fatty acids (SCFA) acetate and propionate. In response to SCFA, may positively regulate renin secretion and increase blood pressure (PubMed:23401498). May also be activated by steroid hormones and regulate cell proliferation (PubMed:19389702). Activated by L-lactate in glomus cells (By similarity). Highly expressed in the prostate (PubMed:11707321). Also expressed in spleen, liver, olfactory epithelium, retinal pigment epithelium and medulla oblongata (PubMed:29249973, PubMed:11707321, PubMed:16491480). In the retinal pigment epithelium expression is restricted to the pigment cells and choroid (at protein level) (PubMed:29249973). Expressed in epidermal melanocytes (at protein level) (PubMed:27226631). Up-regulated in prostate cancer. Belongs to the G-protein coupled receptor 1 family. Contradictory results have been reported for activation of this receptor by beta-ionone in human and mouse. Beta-ionone does not activate OR51E2 in mouse. This difference may depend on the different methods used for the experiment or may be due to species difference.