Cloned receptors for the PP-fold peptides are subdivided into Y1, Y2, PP1/Y4, Y5 and Y6. NPY and PYY have similar affinity for Y1, Y2, Y5 and Y6 receptors while PP has highest affinity for PP1. Pro34-substituted analogs of NPY and PYY have selectivity for Y1 and Y1-like receptors over Y2 receptors. In the present study, we found the putative Y1-selective radioligand, [125I]Leu31, Pro34-PYY, also binds with high affinity to the rat PP1 receptor in cell lines expressing the receptor. However, in rat brain sections, [125I]Leu31, Pro34-PYY does not appear to bind to the interpeduncular nucleus, a brain region containing a high density of [125I]-bPP binding sites. Therefore, it appears there is additional heterogeneity in receptors recognizing PP.
Gehlert, D. R., Schober, D. A., Gackenheimer, S. L., Beavers, L., Gadski, R., Lundell, I., & Larhammar, D. (1997). [125I]Leu31, Pro34-PYY is a high affinity radioligand for rat PP1/Y4 and Y1 receptors: Evidence for heterogeneity in pancreatic polypeptide receptors. Peptides, 18(3), 397–401. https://doi.org/10.1016/S0196-9781(96)00346-4