Receptorphin: A conserved peptide derived from the sequence of the opioid receptor, with opioid displacement activity and potent antiproliferative actions in tumor cells

Table 3 Position of receptorphin in different reported opioid receptor sequences.

Receptor	Source	Length (a.a.)	Receptorphin position	Reference
Delta	Zebrafish	373	90–94	[51]
Delta	Human	372	87–91	[52]
Mu	Human	400	98–102	[53][54][55]
Mu variant	Human	392	107–112	[55]
Mu	Mouse	367	86–90	[56]
Mu	Rat	398	69–100	[57][58][59][60][61][62][63][64]
Mu	Bovine	401	109–113	[65]
Kappa	Rat	380	97–101	[66]
Kappa	Guinea Pig	380	97–101	[67]
Kappa	Mouse	380	97–101	[56]
Kappa	Human	380	97–101	[68][69]
Orphan	Human	370	89–93	[70][71]
Orphan	Rat	357	86–90	[72]
Orphan	Mouse	367	87–92	[56][73][74][75]
Orphan	Rat	367	86–90	[76][77][78][79][80][81]