RESUMEN
These in vitro studies aimed to characterize the pattern and the kinetics of endoproteolysis of the insulinotropic hormone glucagon-like peptide-1 (GLP-1) and related peptides by native ectopeptidases. Peptides were incubated with isolated rat or pig kidney brush-border microvilli membranes, which are a rich source of the ectopeptidases that are responsible for the post-secretory metabolism of peptide hormones. The proteolytic products were separated by reversed-phase HPLC column chromatography and characterised by molecular mass and primary structure. The relative importance of specific peptidases was established by measuring the effects of specific peptidase inhibitors on the kinetics of proteolysis. Dipeptidyl-peptidase-IV was found to be rate-limiting in the endoproteolysis of GLP-1. GLP-1 homologs, exendins-3 and -4, exhibited exceptional stability in the presence of isolated kidney microvilli membranes. Our finding that exendin-4 is several orders of magnitude more stable than GLP-1 and Ser-8-GLP-1 is especially noteworthy given this peptide's widely reported insulinotropic potency.
Asunto(s)
Glucagón/metabolismo , Corteza Renal/enzimología , Fragmentos de Péptidos/metabolismo , Péptidos/metabolismo , Precursores de Proteínas/metabolismo , Animales , Cromatografía Líquida de Alta Presión , Exenatida , Péptido 1 Similar al Glucagón , Cinética , Microvellosidades/enzimología , Péptidos/química , Péptidos/aislamiento & purificación , Ratas , Porcinos , Ponzoñas/metabolismoRESUMEN
This study concerns whether the pancreatic beta cell expresses cell-surface ectopeptidases that are capable of proteolysis of peptide hormones and neuropeptides that modify glucose-dependent insulin release. These biochemical investigations of the RINm5F cell line found that these cells express ectopeptidases. We have characterized the limited endoproteolysis of GLP-1 (7-36) amide that occurs in the presence of RINm5F plasma membranes. The products and the sensitivity to specific peptidase inhibitors of the proteolysis is characteristic of neutral endopeptidase (NEP) 24.11. Vasoactive intestinal polypeptide (VIP), pituitary adenylate cyclase-activating peptide (PACAP), amylin, glucagon, glucose-dependent insulinotropic polypeptide (GIP), and exendin-4 also undergo proteolysis in the presence of RIN cell membranes. NEP 24.11-activity in RIN cell membranes was confirmed using a specific fluorogenic assay, by histochemistry, and by comparison with the recombinant enzyme with respect to the kinetics of proteolysis of GLP-1 (7-36) amide and of a fluorogenic substrate. Specific fluorogenic assays revealed the presence of aminopeptidase N and the absence of aminopeptidase A and of dipeptidylpeptidase IV.
Asunto(s)
Glucagón/metabolismo , Fragmentos de Péptidos/metabolismo , Péptido Hidrolasas/metabolismo , Secuencia de Aminoácidos , Animales , Membrana Celular/enzimología , Hormonas Gastrointestinales , Péptido 1 Similar al Glucagón , Péptidos Similares al Glucagón , Hidrólisis , Insulinoma , Fragmentos de Péptidos/química , Péptido Hidrolasas/química , Ratas , Células Tumorales CultivadasRESUMEN
The post-secretory processing of the potent insulinotropic peptide hormone, GLP-1(7-36)amide, probably involves one or more of a small group of membrane-bound ectopeptidases. Reported here, is the characterisation of the endoproteolysis of human GLP-1(7-36)amide by the recombinant human form of neutral endopeptidase (NEP) 24.11, which is one of the best characterised and widely-distributed of ectopeptidases and is involved in the processing of other peptide hormones. The products of the limited endoproteolysis were characterised by mass and primary structure following fractionation using high performance liquid chromatography. The rate of this endoproteolysis by NEP 24.11 was estimated and compared to that of GLP-1(7-36)amide-related peptides. GLP-1(7-36)amide appears to be good substrate for NEP 24.11 with most, but not all potential target bonds being cleaved. Also, the structurally-related peptides, secretin and glucagon appear to be good substrates whereas GIP and exendin-4 are very poor substrates. That the GLP-1(7-36)amide super-agonist, exendin-4 is a poor substrate for NEP 24.11 is significant for the possible use of this peptide as a prototype for the development of clinically-useful peptide agonists. Further studies should reveal whether NEP 24.11 is important for the metabolic clearance of GLP-1(7-36)amide and will be highly relevant for the attempts to realise the suggested therapeutic value of GLP-1(7-36)amide.