Degussa Aktiengesellschaft

Rolf Wichmann

Christian Wandrey

Wolfgang Leuchtenberger

Maria-Regina Kula

Andreas Buckmann

Ulrich Groeger

Manfred Kircher

Eberhard Breuker

The invention is directed to a method of producing L-amino acids from .alpha.-ketocarboxylic acids by means of continuous fermentation with the aid of glutamate producing bacteria with biomass retention in which the cells are separated by microfiltration and/or centrifugal separators.

Method for the fermentative production of L-amino acids from

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.sup.+ /NADH) enlarged in molecular weight through linkage to a water soluble polymer as coenzyme. Simultaneously NADH is regenerated continuously from NAD.sup.+ 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.sup.+ /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.

Process for the continuous enzymatic change of water soluble

Water soluble .alpha.-ketocarboxylic acids are continuously converted in a membrane reactor into the corresponding aminoacids. The conversion takes place in the presence of a substrate specific dehydrogenase, of ammonium ions and of a nicotinamide-adenine-dinucleotide (NAD.sup.+ /NADH) enlarged in molecular weight through linkage to a water soluble polymer as coenzyme. Simultaneously NADH is regenerated continuously from NAD.sup.+ 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.sup.+ /NADH present bound to a polyoxyethylene 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, an ammonium ion in an amount about equimolar to the amount of substrate 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 aminoacid formed.

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Julich, Germany

Rolf Wichmann