An evaluation of the role of a pyroglutamyl peptidase, a post-proline cleaving enzyme and a post-proline dipeptidyl amino peptidase, each purified from the soluble fraction of guinea-pig brain, in the degradation of thyroliberin in vitro.
The degradation of thyroliberin (less than Glu-His-Pro-NH2) to its component amino acids by the soluble fraction of guinea pig brain is catalysed by four enzymes namely a pyroglutamate aminopeptidase, a post-proline cleaving enzyme, a post-proline dipeptidyl aminopeptidase and a proline dipeptidase. 1. The pyroglutamate aminopeptidase was purified to over 90% homogeneity with a purification factor of 2868-fold and a yield of 5.7%. In addition to catalysing the hydrolysis of thyroliberin, acid thyroliberin and pyroglutamate-7-amido-4-methylcoumarin the pyroglutamate aminopeptidase catalysed the hydrolysis of the peptide bond adjacent to the pyroglutamic acid residue in luliberin, neurotensin bombesin, bradykinin-potentiating peptide B, the anorexogenic peptide and the dipeptides pyroglutamyl alanine and pyroglutamyl valine. Pyroglutamyl proline and eledoisin were not hydrolysed. 2. The post-proline cleaving enzyme was purified to apparent electrophoretic homogeneity with a purification factor of 2298-fold and a yield of 10.6%. The post-proline cleaving enzyme catalysed the hydrolysis of thyroliberin and N-benzyloxycarbonyl-glycylproline-7-amido-4-methylcoumarin. It did not catalyse the hydrolysis of glycylproline-7-amido-4-methylcoumarin or His-Pro-NH2. 3. The post-proline dipeptidyl aminopeptidase was partially purified with a purification factor of 301-fold and a yield of 8.9%. The post-proline dipeptidyl aminopeptidase catalysed the hydrolysis of His-Pro-NH2 and glycylproline-7-amido-4-methylcoumarin but did not exhibit any post-proline cleaving endopeptidase activity against thyroliberin or N-benzyloxycarbonyl-glycylproline-7-amido-4-methylcoumarin. 4. Studies with various functional reagents indicated that the pyroglutamate aminopeptidase could be specifically inhibited by 2-iodoacetamide (100% inhibition at an inhibitor concentration of 5 microM), the post-proline cleaving enzyme by bacitracin (IC50 = 42 microM) and the post-proline dipeptidyl aminopeptidase by puromycin (IC50 = 46 microM). Because of their specific inhibitory effects these three reagents were key elements in the elucidation of the overall pathway for the metabolism of thyroliberin by guinea pig brain tissue enzymes.
D000626:Aminopeptidases / Q000378:metabolism*; D000818:Animals; D001921:Brain / Q000201:enzymology*; D002845:Chromatography / Q000379:methods; D002850:Chromatography, Gel; D004151:Dipeptides / Q000378:metabolism; D018819:Dipeptidyl Peptidase 4; D004152:Dipeptidyl-Peptidases and Tripeptidyl-Peptidases / Q000302:isolation & purification / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D010450:Endopeptidases / Q000302:isolation & purification / Q000378:metabolism*; D006168:Guinea Pigs; D066298:In Vitro Techniques; D007700:Kinetics; D008970:Molecular Weight; D000085822:Prolyl Oligopeptidases; D011751:Pyroglutamyl-Peptidase I / Q000302:isolation & purification / Q000378:metabolism*; D012697:Serine Endopeptidases; D012995:Solubility; D013379:Substrate Specificity; D013973:Thyrotropin-Releasing Hormone / Q000378:metabolism*
D004151:Dipeptides; C019184:histidylprolineamide; D013973:Thyrotropin-Releasing Hormone; D010450:Endopeptidases; D000626:Aminopeptidases; D004152:Dipeptidyl-Peptidases and Tripeptidyl-Peptidases; D018819:Dipeptidyl Peptidase 4; D011751:Pyroglutamyl-Peptidase I; D012697:Serine Endopeptidases; D000085822:Prolyl Oligopeptidases