Pressure effects on the solvent denaturation of NADH*

Nicotinamide adenine dinucleotide (NADH) plays a central role in cellular metabolism as an electron donor via an NAD+/NADH redox reaction. NADH conformational state -- whether it is folded or unfolded -- has physiological significance because it takes on an unfolded conformation when bound to proteins. This study examines the effects of pressure on the solvent denaturation of NADH (20$\mu $M NADH in MOPS buffer solution, pH7.4). Using a quartz capillary-based high-pressure chamber, the folding/unfolding transition of NADH was examined through excited-state emission spectroscopy (337 nm excitation) at physiological pressures up to 50 MPa. By using a two-state solvent-denaturation model to determine thermodynamic parameters of solvent denaturation and by using an Arrhenius relationship, the change in volume for the folding-unfolding reaction is determined.