Characteristics of aminopeptidase activity from bovine brain microvessel endothelium

Blood-brain barrier (BBB) aminopeptidase activity was investigated using an in vitro model consisting of primary cultures of brain microvessel endothelium. Using two different substrates, both membrane-bound and soluble aminopeptidases were found to be associated with brain endothelium. That the enzyme activity was aminopeptidase activity was confirmed with the competitive inhibition of substrate degradation by typical aminopeptidase inhibitors puromycin and bestatin. The aminopeptidase activity was also competitively inhibited by enkephalin, met-enkephalin, and leu-enkephalin. Results from parallel experiments with cerebral gray matter and kidney confirm assay conditions. This report supports previous suggestions that aminopeptidases of the enzymatic BBB may play a role in regulating levels of circulating neuropeptides in the cerebrovasculature.