Three Diverse Alcohol Dehydrogenases Remain Active at Salt Concentrations Greater than 1 M

A comparative study was carried out on the effects of a number of salts on enzyme activity of three representative alcohol dehydrogenases from non-halophilic sources. The enzymes from yeast (YADH), horse liver (HLADH) and Thermoanaerobacter brockii (TBADH) all retain significant activity at concentrations up to 4 M NaCl. In general catalytic activity follows the order NaCl > Na-acetate > Na2SO4 > NaNO3 > NaClO4. The deviation from the normal Hofmeister series may reflect effects in line with the “law of matching water affinity”, based on anion interactions with the Na+ cation in solution or the essential Zn2+ in the enzymes. Retention of activity generally follows the order YADH > HLADH > TBADH, which is opposite to the order of thermostability. Protein structural features promoting thermostability, like additional salt bridges, may lead to greater salt sensitivity. Comparison of cations Cs+, K+, NH4+ and Na+ showed weaker effects, not clearly in line with the Hofmeister series.