BIOTECHNOLOGY - V. H. Herasymenko - 2006

Part II. Special Biotechnologies

Chapter 19. BIOTECHNOLOGY FOR THE PRODUCTION OF L-AMINO ACIDS

19.2. BIOTECHNOLOGY FOR THE PRODUCTION OF L-METHIONINE

Methionine is produced synthetically. D,L-methionine is obtained from acrolein through a rather complex, multi-stage chemical transformation process.

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The production of 1 t of D,L-methionine requires approximately 0.6 t of acrolein. Separation of the racemate is not provided for by the technology. This method accounted for the entire volume of methionine production in the former Soviet Union.

The technology for producing L-methionine using soluble aminoacylase to resolve the racemic mixture was first implemented industrially by the Japanese company Tanabe Seiyaku. In 1969, the company launched large-scale production of L-methionine using aminoacylase immobilized on DEAE-Sephadex in a fixed-bed Reactor.

Commercial aminoacylase preparations are immobilized via adsorption on DEAE-Sephadex through ionic interactions. The immobilization of aminoacylase on DEAE-Sephadex is carried out as follows: 1000 L of Sephadex is stirred for 10 hours with 1100–1700 L of an aqueous enzyme solution (i.e., an enzyme-to-carrier ratio of 1.1–1.7 : 1) at a Temperature of 35 ^oC and pH 7. The mixture is filtered, and the immobilized preparation is washed several times with Water. The activity of the immobilized enzyme is 50–60 % of that of the native enzyme. The half-life of the immobilized aminoacylase under optimal conditions is approximately 65 days. The methionine yield in such a system reaches 91 % of the theoretical value. DEAE-Sephadex can be used in the plant for over 8 years, and catalyst regeneration is performed by adding a fresh aminoacylase solution. The production process is automated.

The concentration of acyl-D,L-methionine in the racemic mixture at the reactor inlet is 0.2 mol/L. The solution enters the reactor from the top at a flow rate of 2000 L/h. After the separation of L-methionine, the remaining unreacted acyl-D-methionine in the solution is racemized to form acyl-D,L-isomers and recycled back for Hydrolysis and isolation of L-methionine.

The advantage of this novel biotechnology lies in its relative simplicity and ease of operation.