| Family | Class A (Rhodopsin) | Class B (Secretin) | Class C (Glutamate) | Adhesion | Frizzled |
|---|---|---|---|---|---|
| Receptors with known ligands | 197a | 15 | 12 | 0 | 11 |
| Orphans | 87 (54)a | – | 8 (1)a | 26 (6)a | 0 |
| Sensory (olfaction) | 390b,c | – | – | – | – |
| Sensory (vision) | 10d opsins | – | – | – | – |
| Sensory (taste) | 30c taste 2 | – | 3c taste 1 | – | – |
| Sensory (pheromone) | 5c vomeronasal 1 | – | – | – | – |
| Total | 719 | 15 | 22 | 33 | 11 |
a
Numbers in brackets refer to orphan receptors for which an endogenous ligand has been proposed in at least one publication, see Davenport et al. (2013)
b
Olender et al. (2008);
c
Mombaerts (2004);
d
Terakita (2005).