Thermodynamic profiles for alcohol dehydrogenase action in free solution

Area of Science:

• Biochemistry and Enzymology
• Chemical Kinetics
• Thermodynamics

Background:

• Alcohol dehydrogenase (ADH) enzymes are crucial in ethanol metabolism.
• Understanding the kinetic and thermodynamic mechanisms of ADH-catalyzed reactions is vital for biochemical research.
• Nicotinamide adenine dinucleotide (NAD) is a key cofactor in redox reactions catalyzed by dehydrogenases.

Purpose of the Study:

• To investigate the reaction kinetics between nicotinamide adenine dinucleotide (NAD) and ethanol catalyzed by yeast alcohol dehydrogenase.
• To determine the thermodynamic profiles of the reaction mechanism.
• To compare the findings with similar lactate dehydrogenase systems.

Main Methods:

• Utilized stopped-flow equipment to monitor reaction rates.
• Measured reaction rates across varying concentrations of NAD and ethanol.
• Analyzed temperature-dependent rate data to obtain thermodynamic profiles.

Main Results:

• The reaction proceeds via an ordered ternary complex mechanism, with NAD binding first.
• Significant negative entropies of activation were observed for NAD and ethanol addition.
• The breakdown of the ternary complex showed a positive entropy of activation, suggesting release of constraints.

Conclusions:

• The observed thermodynamic profiles are consistent with structural constraints during substrate binding.
• These constraints are partially released during the catalytic turnover of the ternary complex.
• The kinetic and thermodynamic patterns are analogous to those observed in lactate dehydrogenase systems.