Figure 1.

Amino acid sequences of the apelin precursor, preproapelin, in cattle, humans, rats, and mice and the molecular forms of apelin detected in vivo. Alignment of preprapelin sequences in cattle, humans, rats, and mice. The arrow indicates the beginning of the sequence of apelin-36 and the apelin-17 (K17F) sequence, strictly conserved in mammals, is underlined. The black dashed boxes show the dibasic doublets that could be recognized by prohormone convertases, potentially involved in preproapelin maturation. The green arrow shows the cleavage site by ACE-2 (EC 3.4.17.23). The blue arrow shows the cleavage site by Neprilysin (EC 3.4.24.11). The various molecular forms of apelin detected in vivo in mammals: apelin-36, apelin-17, and the pyroglutamyl form of apelin-13. Figure adapted from Ref. (11) with permission from the copyright holders.