Figure 1.

Schematic showing 13-/14-mer single letter amino acid sequences for apelin and ELA based peptide ligands respectively. Sequences read from the N-termini (left) to C-termini (right). For apelin tool ligands, methionine (M) was replaced with the non-natural amino acid norleucine (Nle) at position 11, and the C-terminal phenylalanine (F) was replaced with tyrosine (Y) at position 13. pQ denotes the natural pyroglutamate residue found in the endogenous [Pyr¹]apelin-13 peptide. ¹²⁵I denotes the iodine¹²⁵ present at the C-terminus in the [¹²⁵I]-apelin-13 radiolabel. OBn denotes O-benzene. Fluorescent dyes structurally identical to Alexa Fluor 488 and 647 (AF488 and AF647) were conjugated to the N-terminal residues of peptides via a 4-mer polyethylene glycol (PEG4) linker to generate the fluorescent ligands used in this study.