Nonapeptide-1 is an antagonist of melanocortin receptor 1 (MC1R; Ki = 40 nM in COS-1 cells expressing human receptors).1 It is selective for MC1R over MC3R, MC4R, and MC5R (Kis = 470, 1,340, and 2,400 nM, respectively). Nonapeptide-1 inhibits cAMP accumulation and melanosome dispersion induced by α-melanocyte-stimulating hormone (α-MSH) in melanocytes with IC50 values of 2.5 and 11 nM, respectively.2
1.Schi?th, H.B., Muceniece, R., and Wikberg, J.E.S.Characterization of the binding of MSH-B, HB-228, GHRP-6 and 153N-6 to the human melanocortin receptor subtypesNeuropeptides31(6)565-571(1997) 2.Jayawickreme, C.K., Quillan, J.M., Graminski, G.F., et al.Discovery and structure-function analysis of α-melanocyte-stimulating hormone antagonistsJ. Biol. Chem.269(47)29846-29854(1994)