Pyroglutamylated RFamide Peptide (QRFP)

P518 functions as a high-affinity ligand of GPR103. Both GPR103 and P518 precursor mRNA exhibited highest expression in brain.The 43-amino acid QRFP peptide, a longer form of the P518 peptide is necessary to exhibit full agonistic activity with GPR103. Intravenous administration QRFP caused release of aldosterone, suggesting that QRFP and GPR103 regulate adrenal function.The deduced 126-amino acid protein contains a putative N-terminal 22-amino acid signal peptide and no transmembrane domain, suggesting that the protein or cleavage products can be secreted. The 26-amino acid P518 peptide sequence is located at the C terminus of the precursor protein. In peripheral tissues, P518 precursor mRNA was detected in prostate, testis, colon, thyroid, parathyroid, coronary artery, and bladder.