Stabilization of the structure and activity of yeast carboxypeptidase Y by its high-mannose oligosaccharide chains

Sodium dodecyl sulfate was shown to promote both the inactivation and proteolytic degradation of the yeast glycoprotein, carboxypeptidase Y, with the former effect occurring six times faster than the latter. Although the proteolysis, as judged by polyacrylamide gel electrophoresis, was inhibited by pepstatin, which implicates the presence of proteinase A, the possibility of autodigestion could not be ruled out. A contributing role of the enzyme's carbohydrate moiety to these two processes was revealed by treating carboxypeptidase Y with endo-β-N-acetylglucosaminidase H. This treatment removes all four of the enzyme's Oligosaccharide chains in sodium dodecyl sulfate and as a consequence increases the rate of inactivation of the resulting carboxypeptidase Y by twofold and its proteolytic degradation by threefold relative to that of untreated enzyme. It thus appears that carboxypeptidase Y is a glycoprotein whose structural integrity and functional activity are influenced by its associated carbohydrate component.