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The role of hydration in enzyme activity and stability: 2. Alcohol dehydrogenase activity and stability in a continuous gas phase reactor

The degree of enzyme hydration is the one of the most important factors which can affect enzyme activity and stability in water‐limited environments. Alcohol dehydrogenase from baker's yeast (YADH) has been used as a model enzyme to study the effects of hydration on activity, stability, and cofactor stability with gas phase substrates. In all cases, the enzyme is essentially inactive until a temperature‐independent degree of surface coverage by water molecules has been reached. The critical water content corresponds to 40–50% of a single monolayer. Careful control of the degree of hydration, by adjustments to gas humidity and temperature, enables the enzyme to be stabilized for periods exceeding 1 month, whereas in water the half‐life of the enzyme is 30 min. The reaction with gas phase substrates follows a pseudo‐first‐order mechanism with an activation energy of 7.5 ± kcal/mol, which is almost half of that in aqueous solution. © 1996 John Wiley & Sons, Inc.