Stability of [D-Trp11]-neurotensin to rat brain peptidases

The stability of neurotensin (NT) and a potent, long lasting analogue, [D-Trp11]-NT, to rat brain peptidases was compared by incubating the peptides with subcellular fractions (synaptosomes, synaptic membranes) and a purified endopeptidase from rat brain. Degradation of the peptides with time was followed by high performance liquid chromatography (HPLC). The rates of degradation (pmol/min/mg prot.) in synaptosomes were 890 (NT) and 59 [D-Trp11]-NT), and in synaptic membranes were 1180 (NT) and 12 ([D-Trp11]-NT). The main products of the degradation of [D-Trp11]-NT by synaptic peptidases (isolated by HPLC and characterized by amino acid analysis) were the 1-3, 1-4 and 6-13 fragments implying cleavage of [D-Trp11]-NT at the Tyr3-Glu4, Glu4-Asn5 and Asn5-Lys6 bonds. The rates of degradation of NT and [D-Trp11]-NT by the purified endopeptidase from rat brain were 27.2 and 0.76 pmol/min/microliter of enzyme solution respectively. This endopeptidase, which hydrolyses NT at Arg8-Arg9, may be responsible along with other endopeptidases for NT degradation at nerve terminals.