Alpha-bag cell peptide [
alpha-BCP (
Ala-Pro-Arg-Leu-Arg-Phe-Tyr-Ser-Leu)] is a
neurotransmitter that mediates bag cell-induced inhibition of left-upper-quadrant (LUQ) neurons L2, L3, L4, and L6 in the abdominal
ganglion of Aplysia. Our recent biochemical studies have shown that
alpha-BCP[1-9] is cleaved into
alpha-BCP[1-2], [3-9], [1-5], [6-9], and [7-9] by a combination of three distinct
peptidase activities located within the extracellular spaces of the CNS: A diaminopeptidase-IV (DAP-IV)-like
enzyme cleaves
alpha-BCP[1-9] at the 2-3
peptide bond; a neutral
metalloendopeptidase (NEP)-like
enzyme cleaves either
alpha-BCP[1-9] or
alpha-BCP[3-9] at the 5-6 bond; an
aminopeptidase M-II (APM-II)-like
enzyme cleaves
alpha-BCP[6-9] at the 6-7 bond, but cleaves neither
alpha-BCP[1-9], nor the other ganglionic
peptidase products. To further understand the manner in which
alpha-BCP is inactivated after release, that is loses its electrophysiological activity, we studied its structure-activity relationship by recording intracellularly from LUQ neurons in isolated abdominal ganglia that were arterially perfused with
peptides dissolved in artificial sea water. The effects of
alpha-BCP[1-9] and 15 of its fragments ([1-8], [1-7], [1-6], [1-5], [2-9], [3-9], [3-8], [6-9], [7-9], [8-9], [6-7], [6-8], [1-2], Phe, Tyr) indicated that the sequence Phe6-Tyr7 was both necessary and sufficient to produce LUQ inhibitory activity.(ABSTRACT TRUNCATED AT 250 WORDS)