Action of three ectopeptidases on corticotropin-releasing factor: Metabolism and functional aspects

Using purified enzyme preparations, we investigated the actions of angiotensin-converting enzyme, aminopeptidase N, and endopeptidase 24.11 on corticotropin-releasing factor (CRF). The effects of inhibition of these enzymes on CRF action in rat anteriorpituitary cultures were also determined. Finally, specific inhibitors were used to evaluate ectopeptidase action on the regionalbrainmetabolism of CRF. Km values for CRF were 165, 90, and 42 μM for angiotensin-converting enzyme, aminopeptidase N, andendopeptidase 24.11, respectively. A CRF metabolite profile for each enzyme was determined. In pituitary cultures, inhibition ofendopeptidase 24.11 and aminopeptidase N potentiated CRF-stimulated release of adrenocorticotropic hormone (ACTH). In ratpituitary and hypothalamus membrane preparations, specific inhibitor experiments indicated that CRF hydrolysis involved members ofthe neutralendopeptidase and aminopeptidase enzyme families. In cortex membranes, similar peptidase inhibition was without effect.These data support the hypothesis that ectopeptidases play a major role in CRF metabolism and biological function.