Immobilized microbial nitrilase for production of glycolic acid
View Patent ↗The present invention provides a process for preparing an enzyme catalyst having nitrilase activity for hydrolysis of glycolonitrile to glycolic acid with improved retention of recovered catalyst activity in consecutive batch reactions with catalyst recycle, said process comprising pretreating the enzyme catalyst with glutaraldehyde. The glutaraldehyde-pretreated enzyme catalyst has improved specific activity when compared to non-glutaraldehyde-pretreated enzyme catalysts, and thereby, has improved overall catalyst activity and productivity.
1. A process for improving the retention of the initial specific activity of an enzyme catalyst having nitrilase activity during the conversion of glycolonitrile to glycolic acid, said process comprising:
(a) producing an enzyme catalyst having nitrilase activity by fermentation, said enzyme catalyst comprising a polypeptide having an amino acid sequence selected from the group consisting of SEQ ID NOs: 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 27, 29, 31, 33, 35, 37, 39, 41, 43, 45, 47, 49, 51, 53, 55, and 57;
(b) pretreating said enzyme catalyst with glutaraldehyde;
(c) optionally inactivating unreacted glutaraldehyde with bisulfite following glutaraldehyde pretreatment;
(d) recovering the enzyme catalyst from (b) or (c) and immobilizing said enzyme catalyst in carrageenan;
(e) cross-linking the resulting carrageenan-immobilized enzyme catalyst of (d) with glutaraldehyde and polyethylenimine; and
(f) producing a glutaraldehyde-pretreated immobilized and cross-linked enzyme catalyst, wherein said glutaraldehyde-pretreated immobilized and cross-linked enzyme catalyst has improved retention of initial specific activity during conversion of glycolonitrile to glycolic acid as compared to non-glutaraldehyde-pretreated immobilized and cross-linked enzyme catalysts under the same reaction conditions.
2. The process of claim 1 wherein the pH is maintained between 5.0 and 9.0 during pretreatment with glutaraldehyde.
3. The process of claim 1 wherein the pretreating with glutaraldehyde in step (b) comprises adding glutaraldehyde to a fermentation broth produced by step (a) in an amount in the range of about 3 g/L (0.025 g GA per OD 550 ) and about 5 g/L (0.042 g GA per OD 550 ).
4. The process of claim 1 wherein the pretreating with glutaraldehyde in step (b) comprises adding glutaraldehyde to a fermentation broth produced by step (a) at a rate of 50 mg/L/h to 500 mg/L/h.
5. An isolated glutaraldehyde pretreated, immobilized and cross-linked enzyme catalyst produced by the process of claim 1 .
6. The enzyme catalyst of claim 5 , wherein said catalyst retains at least about 70% of its initial specific activity after at least four consecutive batch recycle reactions.