Octyl Glucoside Induced Formation of the Molten Globule-Like State of Glutamate Dehydrogenase

The interaction between n-octyl-β-D-glucopyranoside (octyl glucoside) and bovine liver glutamate dehydrogenase (GDH) was studied using techniques including equilibrium dialysis, UV-spectrophotometry, circular dichroism (CD), fluorescence energy transfer and extrinsic spectrofluorometry in 50 mM sodium phosphate buffer solution (pH 7.6). The equilibrium dialysis experiment showed a higher binding of octyl glucoside to GDH that induces up to 80% enzyme inhibition in 20 mM octyl glucoside solution. The CD study indicated that GDH retains its secondary structure in the presence of octyl glucoside, but loses a degree of its tertiary structure by acquiring a more extended tertiary structure. Measurement of the binding of a hydrophobic fluorescent probe, 1-anilino-naphthalene-8-sulfonate (ANS), to GDH revealed that the binding of ANS to GDH is increased in the presence of octyl glucoside, a finding that may be interpreted in terms of the increment of surface hydrophobic patch(es) of GDH because of its binding to octyl glucoside. Fluorescence energy transfer studies also showed more binding of the reduced coenzyme (NADH) to GDH and the Lineweaver-Burk plots (with respect to NADH) indicate the existence of substrate inhibition in the presence of octyl glucoside. These observations are aimed at explaining the formation of the molten globule-like structure of GDH, which is induced by a non-ionic detergent such as octyl glucoside.