PACAP-38 is a chemorepellent and an agonist for the lysozyme receptor in Tetrahymena thermophila

Pituitary adenylate cyclase activating peptide (PACAP-38) is a peptide horm one which functions in many mammalian systems, including the nervous and di gestive systems. Using in vivo behavioral studies, we have found that this hormone functions as a chemorepellent in Tetrahymena thermophila with an EC 50 of 10 nM. Cells previously adapted to PACAP-38 were found to be adapted to lysozyme, and vice versa. Furthermore, the in vivo behavioral activity o f PACAP-38 was blocked by addition of the anti-lysozyme receptor antibody. 5545. Chemorepellent activity of PACAP-38 was also inhibited by the additio n of neomycin sulfate (inhibition constant K-i = 0.080 mu mol.l(-1)), a com petitive inhibitor of lysozyme binding to its receptor. PACAP-38 is a more potent and specific agonist for the lysozyme receptor than either intact ly sozyme or CB2, a 24-amino acid fragment of lysozyme.