PMID: 2113524Jul 5, 1990Paper

Identification of an active-site residue in yeast invertase by affinity labeling and site-directed mutagenesis.

The Journal of Biological Chemistry
V A Reddy, F Maley

Abstract

Deglycosylated yeast invertase is irreversibly inactivated by conduritol B epoxide (CBE), an active-site-directed reagent. The inactivated enzyme contained 0.8 mol of CBE/mol of invertase monomer suggesting that the inactivation results from the modification of a single amino acid residue. Peptic digestion of [3H]CBE-labeled invertase followed by reverse phase column chromatography yielded two labeled peptides, both located at the amino-terminal end of the enzyme. Sequence analyses of these peptides revealed that Asp-23 is the modified residue. The role of Asp-23 in the catalytic process was investigated by changing it to Asn using site-directed mutagenesis of the SCU2 gene. The mutant enzyme was basically inactive, confirming a role for Asp-23 in the catalytic process.

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