Optimization of an immobilized-cell biocatalyst for production of 4-cyanopentanoic acid

Optimization of microbial cell immobilization, catalyst specific activity, and volumetric productivity were required for scale-up of the nitrilase-catalyzed hydrolysis of 2-methylglutaronitrile to 4-cyanopentanoic acid, an intermediate in the preparation of 1,5-dimethyl-2-piperidone. As an alternative to the immobilization of Acido vorax facilis 72W cells in carrageenan, immobilization in alginate, followed by cross-linking with glutaraldehyde and polyethylenimine, produced a catalyst which was stable in reaction mixtures containing high concentrations of 4-cyanopentanoic acid ammonium salt. Immobilization in alginate produced catalysts with a higher nitrilase specific activity than was achieved in carrageenan, and volumetric productivity of 4-cyanopentanoic acid was increased from 19 to 49 g/L/h. Substituting alginate for carrageenan also eliminated one process step in the immobilization. A further increase in volumetric productivity to 79 g/L/h was achieved by using an immobilized Escherichia coli transformant which expresses A. facilis 72W nitrilase.