CHARACTERIZATION OF THE PROCESSING BY HUMAN NEUTRAL ENDOPEPTIDASE-24.11 OF GLP-1(7-36) AMIDE AND COMPARISON OF THE SUBSTRATE-SPECIFICITY OFTHE ENZYME FOR OTHER GLUCAGON-LIKE PEPTIDES

The post-secretory processing of the potent insulinotropic peptide hor mone, GLP-1(7-36)amide, probably involves one or more of a small group of membrane-bound ectopeptidases. Reported here, is the characterisat ion of the endoproteolysis of human GLP-1(7-36)amide by the recombinan t human form of neutral endopeptidase (NEP) 24.11, which is one of the best characterised and widely-distributed of ectopeptidases and is in volved in the processing of other peptide hormones. The products of th e limited endoproteolysis were characterised by mass and primary struc ture following fractionation using high performance liquid chromatogra phy. The rate of this endoproteolysis by NEP 24.11 was estimated and c ompared 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 pot ential target bonds being cleaved. Also, the structurally-related pept ides, secretin and glucagon appear to be good substrates whereas GIP a nd 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 f or 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 s uggested therapeutic value of GLP-1(7-36)amide.