Prokineticin receptors, PKR1 and PKR2 (provisional nomenclature as recommended by NC-IUPHAR [23]) respond to the cysteine-rich 81-86 amino-acid peptides prokineticin-1 (also known as endocrine gland-derived vascular endothelial growth factor, mambakine) and prokineticin-2 (protein Bv8 homologue). An orthologue of PROK1 from black mamba (Dendroaspis polylepis) venom, mamba intestinal toxin 1 (MIT1, [65]) is a potent, non-selective agonist at prokineticin receptors [41], while Bv8, an orthologue of PROK2 from amphibians (Bombina sp., [44]), is equipotent at recombinant PKR1 and PKR2 [48], and has high potency in macrophage chemotaxis assays, which are lost in PKR1-null mice.