Biotransformation of Nitriles and Alcohols to Carboxylic Acids Using Industrial Enzymes
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Nitrilases (EC 184.108.40.206) hydrolyze nitriles to corresponding carboxylic acids and ammonia while alcohol oxidases (EC 220.127.116.11) and alcohol dehydrogenases (EC 18.104.22.168) oxidize alcohols to aldehydes using molecular oxygen and NAD+ as oxidants, respectively. In this study, the enzyme activity of nitrile and alcohol substrates from Huntsman LLC, The Woodlands, TX was investigated. Alcohol dehydrogenase from both yeast and equine liver did not react with Huntsman’s alcohols LI and L2. The alcohol oxidase, however, showed increasing activity for the alcohols A3, A2 and Al, respectively.
The nitrilase reaction turned over 150 pM of products in 4 hours at the optimum pH (7.5) and temperature (25 °C) of the enzyme. The effects of temperature and pH on the stability of the nitrilase as well as catalysis in organic solvents were also studied. The enzyme exhibited high thermal stability between 25 °C- 40 °C. At 50 °C, activity decreased to 50% with complete loss of activity occurring at temperatures above 60 °C. Slightly alkaline and neutral pH environments also improved enzyme stability. These pH ranges are consistent with values reported in the literature. The incorporation of the organic solvents, methanol and ethanol at 80% (v/v), into the reaction denatures the enzyme and little or no activity was observed. However, low ethanol concentrations (10% v/v) increased the enzyme activity to 120% relative to the standard reaction (no organic solvent) by increasing the solubility of the hydrophobic nitrile. In addition, the enzyme appears to be more stable in ethanol than methanol. A comparison of enzyme activity for benzonitrile and Huntsman’s nitrile (aliphatic) suggests that the enzyme is more efficient in hydrolyzing aromatic nitriles than aliphatic nitriles.
CitationAgbley, G. (2013). Biotransformation of nitriles and alcohols to carboxylic acids using industrial enzymes (Unpublished thesis). Texas State University, San Marcos, Texas.
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