Rat brain and kidney metalloendopeptidase: Enkephalin heptapeptide conversion to form a cardioactive neuropeptide,Phe-Met-Arg-Phe-Amide

Rat brain or kidney metalloendopeptidase purified from particulates cleaved Met-enkephalin-Arg⁶-Phe⁷ and its amide at the Gly³-Phe⁴ bond to release Phe-Met-Arg-Phe or the tetrapeptide amide. The latter, a neuropeptide with cardioactive properties, was relatively stable upon further incubation. The metallo-nature of the enzyme was established by inhibition with chelating agents (EDTA, o-phenanthroline) and its endopeptidase nature by cleavage at the Gly³-Phe⁴ bond of pentapeptide enkephalins or precursors such as the heptapeptide, or analogs bearing N- or C-terminal protective groups. Presence of C-terminal amides decreased the rate of hydrolysis. Thiorphan, (DL-3-mercapto-2-benzylpropanoyl)-glycine, competitively inhibited cleavage at the Gly³-Phe⁴ bond of enkephalin (Ki 10 nM). The thiorphan sensitive metalloendopeptidase provides a pathway for conversion of an enkephalin precursor to form a non-opioid peptide of biological interest.