Subchapter 52C – Pyrokinin

PKs and MTs were first discovered in the cockroach and locust as relatively small peptides that control hindgut contraction. These peptides share a common C-terminal sequence FXPRL-NH2 but have variable N-terminal sequence and peptide length. Similar peptides with the same C-terminal motif have been identified in moths and the fruit fly Drosophila melanogaster. In Drosophila, MT-I (CAPA-PK) and -II (PK2) are encoded by the capa gene and hugin gene, respectively. Drosophila MT-I is also similar to diapause hormone (DH), because both peptides share the same C-terminal WFXPRLamide motif (DH signature). Two classes of PK/MT receptors have been identified in Drosophila: PK1/DH receptor, and two PK2/PBAN receptors. The PK1/DH receptor shows higher affinity to Drosophila MT-I and DH than to MT-II and cockroach PK, while the PK2/PBAN receptors exhibit higher affinity to MT-II and cockroach PK than to MT-I and DH.