Effect of oligosaccharides and chloride on the oligomeric structures of external, internal, and deglycosylated invertase

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Abstract
External invertase exists in an oligomeric equilibrium of dimer, tetramer, hexamer, and octamer, the concentrations of which vary with pH, time, and concentration of enzyme [Chu, F. K., Watorek, W., and Maley, F. (1983) Arch. Biochem. Biophys. 223, 543-555; Tammi, M., Ballou, L., Taylor, A., and Ballou, C. E. (1987) J. Biol.Chem. 262, 4395-4401]. To assess the influence of carbohydrate on this equilibrium, we investigated the self-association of external invertase (10 oligosaccharides per subunit), deglycosylated external invertase (2 oligosaccharides per subunit), and internal invertase (no carbohydrate) under various conditions. In addition, the effect of carbohydrate on the interaction of the subunits of these various invertases to form heterooligomers was studied. Chloride ion was found to promote subunit association in the various invertases irrespective of their glycosylation status. However, external invertase was less responsive to chloride ion relative to the internal and deglycosylated invertases. The higher oligomers of deglycosylated invertase were stable at 47.degree. C whereas those of external invertase dissociated rapidly into dimers, suggesting that the additional oligosaccharides in external invertase destabilize subunit interaction. Hybridization experiments with the various invertases showed that the dimers of internal invertase formed heterooligomers with either external or deglycosylated invertase. By contrast, the monomers of external and internal invertases formed their respective homodimers, but not heterodimers. These results suggest that the oligosaccharide content of invertase not only influences the extent of self-association but also affects heterooligomer formation.