title: Carboxypeptidase Y from Saccharomyces cerevisiae. Conformational differences reflected in kinetic behaviour in water and deuterium oxide.
abstract: The glycoenzyme carboxypeptidase Y (peptidyl--amino-acid hydrolase, EC 3.4.16.1), from baker's yeast (British Fermentation Products Strain, Ng 72), of molecular weight 60 000, had a protein portion closely similar to those in the literature for carboxypeptidase Y isolations from other yeast sources, but was 25.3 wt% carbohydrate (mannose 83.3% by wt., glucosamine 10.3% by wt. with traces of galactose and galactosamine). Circular dichroic spectra indicated that the enzyme lost its beta-structure as the pH was lowered from 8.08 to 4.16. At p2H 8.22 in 2H2O media the conformation of this enzyme was different from that observed at pH 8.08. A tyrosine residue appeared to be perturbed by lowering the pH of the medium. Carboxypeptidase Y was rapidly, and essentially irreversibly, inactivated at low p2H. The pH profile of kcat for the carboxypeptidase Y-catalysed hydrolysis of 4-nitrophenyltrimethylacetate showed two inflections at 45 degrees C: one at pKapp approximately 3.7 insensitive to temperature variation (ascribed to a carboxyl group), and one of pKapp approximately 5.7 markedly temperature-dependent and possibly caused by a histidine residue.
mesh_terms: D002268:Carboxypeptidases; D043402:Cathepsin A; D055598:Chemical Phenomena; D002621:Chemistry; D002942:Circular Dichroism; D003903:Deuterium; D017666:Deuterium Oxide; D007700:Kinetics; D008970:Molecular Weight; D012441:Saccharomyces cerevisiae / Q000201:enzymology*; D029701:Saccharomyces cerevisiae Proteins; D013329:Structure-Activity Relationship; D014867:Water
chemical_list: D029701:Saccharomyces cerevisiae Proteins; D014867:Water; D003903:Deuterium; D002268:Carboxypeptidases; D043402:Cathepsin A; C499283:PRC1 protein, S cerevisiae; C022633:serine carboxypeptidase; D017666:Deuterium Oxide