Table 1..

GPCR groups of the rhodopsin family used in this study. Adapted from Joost and Methner (2002).

GPCR group	Receptor ligand types
group 1	CC chemokines
group 2a	CXC chemokines
group 2b	duffy
group 3	angiotensin, apelin, bradykinin
group 4	opioids, neuropeptide B, nociceptin, somatostatin
group 5	galanin, melanin-concentrating hormone, kisspeptin, leukotriene-B4, somatostatin, urotensin
group 6a	cholecystokinin, gastrin, neuropeptide FF, orexin
group 6b	gonadotrophin-releasing hormone, vasopressin
group 6c	orphan
group 7a	bombesin, endolethin, gastrin-releasing peptide, neuromedin B
group 7b	growth hormone secretagogue, neuromedin U, neurotensin, motilin, thyrotropin-releasing hormone
group 8a	anaphylatoxin, lipoxin A4, N-formyl peptide
group 8b	mas
group 9a	substance-P, substance K, neuromedin K
group 9b	prolactin-releasing peptide, melatonin, neuropeptide Y, prokineticin
group 10	follitropin, thyrotropin, thyrotropin-releasing hormone, lutropinchoriogonadotropic
group 11	lipids, proprionate, short chain fatty acids, nicotinic acid, ATP
group 12	UDP-glucose, ADP, platelet activating factor
group 13	adrenocorticotropic hormone, cannnabinoid, sphingosine 1-phosphate, lysophosphatidic acid, sphingolipid, melanotropin
group 14	prostaglandin, prostacyclin, thromboxane
group 15	lysophosphatidylcholine, psychosine, thrombin, proteinase
group 16	opsins, peropsin
group 17	5-hydroxytryptamine, adrenergic, dopamine, histamine H2
group 18a	muscarinic acetylocholine, histamine, H2
group 18b	adenosine
groups18c-i	orphan
group 19	5-hydroxytryptamine