Process for the continuous enzymatic change of water soluble alpha -ketocarboxylic acids into the corresponding alpha -hydroxycarboxylic acids

摘要

Water soluble alpha -ketocarboxylic acids are continuously converted in a membrane reactor into the corresponding alpha -hydrocarboxylic acids. The conversion takes place in the presence of a substrate specific dehydrogenase and of a nicotinamide-adenine-dinucleotide (NAD+/NADH) enlarged in molecular weight through linkage to a water soluble polymer as coenzyme. Simultaneously NADH is regenerated continuously from NAD+ in presence of a formate dehydrogenase and from formate ion. The membrane must have a mean pore diameter of 1 to 3 nm. As coenzyme there is employed 0.1 to 10 mmol/l of NAD+/NADH present bound to a water soluble polymer having an average molecular weight between 500 and 50,000. There is continuously supplied to the reactor a substrate stream which contains 50 to 100% of the maximum amount soluble, but not over 2,000 mmol/l, of the reacting alpha -ketocarboxylic acid in the form of a water soluble salt and 100 to 6,000 mmol/l of a formate. There is maintained over the membrane a differential pressure of 0.1 to 15 bar. There is continuously drawn off behind the membrane a filtrate stream containing the alpha -hydroxy acid formed.