Abstract: Membrane vesicles, showing a 21 ± 2‐fold enrichment in the activity of 5′‐nucleotidase and a 11 ± 4‐fold enrichment in the activity of angiotensin‐converting enzyme relative to homogenate, were prepared from the myenteric plexus‐containing longitudinal muscle layer of guinea pig ileum. Incubation of the vesicles with substance P and neurokinin A led to degradation of the peptides, and metabolites were isolated by reverse‐phase HPLC and identified by amino acid composition. Cleavages of substance P between Glu6‐Phe7, Phe7‐Phe8, and Gly9‐Leu10 and of neurokinin A between Gly8‐Leu9 were observed and could be inhibited in a dose‐dependent manner by phosphoramidon, an inhibitor of neutral endopeptidase 24.11. Formation of these metabolites was not completely inhibited by this agent, indicating that a phosphoramidon‐insensitive form of endopeptidase 24.11 was present in the gut. Substance P was resistant to degradation by aminopeptidases, but neurokinin A was a substrate for bestatin‐sensitive aminopeptidase(s), so that the neurokinin A (3–10) fragment represented the predominant metabolite in the chromatograms. The rate of formation of all the metabolites was not inhibited by ena‐lapril and not enhanced by an increased Cl− concentration, indicating that angiotensin‐converting enzyme was unimportant in the degradation process. Degradation of neurokinin A by the vesicles (Km 30 μM; Vmax 7.2 ±0.8 nmol min−1 mg of protein−1) was more rapid than degradation of substance P (Km 25 μM; Vmax 4.4 ± 0.4 nmol min−1 mg of protein−1).
|Number of pages||9|
|Journal||Journal of Neurochemistry|
|Publication status||Published - 1 Jan 1986|
- Endopeptidase 24.11
- Membrane vesicle
- Neurokinin A
- Substance P