Figure 1: Orexin A and orexin B are derived from a common precursor peptide, prepro-orexin. The actions of orexins are carried out thanks to two receptors that have G protein denominated OXR-1 and OXR-2 receptors. OXR-1 is selective for orexin A, while OXR-2 shows similar affinity for both orexin A and orexin B. OXR-1 is coupled to the Gq subclass of heterotrimeric G proteins, while OXR-2 couples to Gi/o and /or GQ cell lines.