Characterization of a neutral, divalent cation-sensitive endopeptidase: a possible role in neuropeptide processing.

A trypsin-like endopeptidase which cleaves the synthetic substrate Dansyl-Phe-Leu-Arg-Arg-Ala-Ser-Leu-Gly-COOH (Dansyl-Phe-Kemptide) primarily at the Arg4-Ala5 bond has been partially purified from bovine adrenal chromaffin granules, brain and liver. The enzyme appears to have a relatively homogeneous tissue distribution, although highest levels were found in brain regions such as the hippocampus and corpus striatum. Sucrose density gradient fractionation established that enzyme activity assayed at pH 8.5 is not associated with lysosomes. Purified enzyme displays a dimeric structure with subunit molecular weights of 40 kDa and 42 kDa and a native molecular weight of 85,000 Da. The endopeptidase has a neutral pH optimum, is sensitive to divalent cations and thiol reagents, and can cleave on either the amino or carboxyl side of some but not all internal basic amino acids.