Influence of polyol additive on enzyme catalytic selectivity towards different substrates

Area of Science:

• Biochemistry
• Enzyme kinetics
• Biocatalysis

Background:

• Yeast alcohol dehydrogenase (yADH) is a crucial enzyme in metabolic pathways.
• Understanding enzyme behavior in the presence of additives like sorbitol is important for biocatalysis.
• Water activity depressors can significantly influence enzyme performance.

Purpose of the Study:

• To investigate the effect of sorbitol on the kinetic behavior of yADH.
• To determine how sorbitol modifies enzyme activity and substrate selectivity.
• To elucidate the opposing mechanisms through which sorbitol influences yADH.

Main Methods:

• Enzyme kinetic assays were performed using yADH with various alcohol substrates (ethanol, propanol, butanol, pentanol) and the coenzyme NAD.
• The concentration of sorbitol was varied to observe its impact on kinetic parameters.
• Apparent Michaelis constant (Km) values were analyzed.

Main Results:

• Sorbitol addition decreased apparent Km values for all alcohol substrates and NAD, indicating increased substrate affinity.
• The influence of sorbitol on enzyme activity varied with the carbon-chain length of the alcohol substrate, altering catalytic selectivity.
• Observed effects suggest a combination of sorbitol's positive impact (enhanced substrate accessibility) and negative impact (diffusional constraints).

Conclusions:

• Sorbitol acts as a modulator of yADH's kinetic properties.
• The enzyme's catalytic selectivity is significantly altered by sorbitol in a substrate-dependent manner.
• Sorbitol's dual effects on enzyme conformation and substrate diffusion explain the observed kinetic modifications.