Glucoamylase (a-1,4-glucan glucohydrolase, EC 3.2.1.3) is an inverting exohydrolase, that catalyzes the release of b-glucose from the non reducing end of maltodextrin chains. Glucoamylase is inhibited by the sugar analog acarbose which binds to the active site. We are interested in conducting differential scanning calorimetry (DSC) measurements to investigate the stability of glucoamylase and mutants thereof. Glucoamylase is not reversible, but we would like to extract as much thermodynamic information as possible from a series of DSC experiments. Acarbose is a very tight inhibitor (KA = 1012 M) and by utilizing isothermal titration calororimetry (ITC) the degree of protonation, the pKA , the enthalpy and the heat capacity of binding will be obtained. We are working with glucoamylase from Aspergillus niger and the structure of a closely related glucoamylse from Aspergillus awamori var. X100 complexed with acarbose. By investigating the surface area changes upon binding and utilizing the recently developed thermodynamic structural parameterization, estimates will be made of the relevent thermodynamic quantities. These values will be compared to those found experimentally.
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