The stability of yeast invertase is not significantly influenced by glycosylation.

Yeast invertase exists in two different forms. The cytoplasmic enzyme is nonglycosylated, whereas the external invertase contains about 50% carbohydrate of the high mannose type. The protein moieties of both enzymes are identical. The two invertases have been used previously as a model system to investigate the influence of covalently linked carbohydrate chains on the stability of large glycoproteins, and controversial results were obtained. Here, we measured thermal and denaturant-induced unfolding by various probes, such as the loss of enzymatic activity, and by the changes in absorbance and fluorescence. The ranges of stability of the two invertases were found to be essentially identical, indicating that the presence of a high amount of carbohydrate does not significantly contribute to the stability of external invertase. Earlier findings that invertase is stabilized by glycosylation could not be confirmed. The stability of this glycoprotein is apparently determined by the specific interactions of the folded polypeptide chain. Unlike the glycosylated form, the carbohydrate-free invertase is prone to aggregation in the denatured state at high temperature and in a partially unfolded form in the presence of intermediate concentrations of guanidinium chloride.