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Date of Award

2006

Document Type

Restricted Thesis: Campus only access

Degree Name

Bachelor of Science

Department

Biochemistry & Molecular Biol.

First Advisor

J. Ellis Bell

Abstract

Bovine Glutamate Dehydrogenase (GDH) is subject to extensive allosteric regulation and requires substrate induced subunit interactions for maximum catalytic activity. In this investigation, guanidine hydrochloride unfolding, heat inactivation, and differential scanning calorimetry (DSC) experiments were conducted to examine the effect of ligands on GDH conformational stability and enzyme flexibility. The results of these experiments were correlated with previous studies on the effects of ligand induced conformational changes, cofactor binding, and overall activity. Without ligands, GDH can be thought of as poised to allow subunit interactions. Substrates which do not trigger or block cooperative interactions lead to enhanced stability, while ligands permitting efficient catalysis or enhancing catalysis were shown to increase flexibility. Particularly, studies show ADP and norvaline greatly stabilize the enzyme: ADP has previously been demonstrated to block subunit communication while norvaline is known to prevent subunit communication. Furthermore, NADPH, which only binds to the active site, makes GDH less stable than NAD(H), which has been shown to first bind the ADP binding site and then to the active site. Strength of the subunit interfaces of the GDH hexamer was investigated in GuHCl experiments; the study revealed that norvaline greatly stabilizes all interfaces while other ligands have moderate effects on either the trimer-trimer or the monomer-monomer subunit interactions. From these experiments a pattern emerges of ligands stabilizing GDH conformation, acting to block subunit interactions, and inhibiting the overall activity, or ligands increasing conformational flexibility, promoting subunit interactions, and allowing part of the binding energy to promote catalysis through subunit interactions.

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