Effect of chain length on the activity of free and immobilized alcohol dehydrogenase towards aliphatic alcohols

As long-chain alcohol dehydrogenases are not easily available and seldom reported enzymes, it is worthwhile to appraise the potential of well known dehydrogenases, like horse liver alcohol dehydrogenases (HLAD), for the oxidation of long-chain aliphatic alcohols. Oxidation of docosanol (C₂₂) and tetracosanol (C₂₄) is of technological relevance within an industrial platform for the fractionation and upgrading of tall-oil from the Kraft pulping process. Results are presented on the characterization of free and immobilized HLAD with respect to their potential for oxidizing long-chain aliphatic alcohols. Enzyme activity with respect to chain length and pH is presented. Activity for both free and immobilized HLAD increased with pH up to 8.8, but behavior with respect to chain length varied from one biocatalyst to the other. Even though both biocatalysts were less active towards very long-chain aliphatic alcohols, immobilized HLAD had an activity on docosanol and tetracosanol higher than 50% of the value obtained with ethanol, butanol and octanol, which is encouraging and has not been previously reported. Investigation on thermophilic sources and further immobilization strategies are underway to obtain more active and stable catalysts amenable for working at high temperatures which is quite relevant in this case due to the poor solubility of substrates.