Hydantoinase carbamoylase

Recently, recombinant biocatalysts obtained using Escherichia coli cells were designed for this process. The overexpression of all enzymes required for the process, namely, hydantoinase, carbamoylase, and hydantoin racemase from Arthrobacter sp. DSM 9771 was achieved. These cells were used for production of a-amino acids at the concentration of above 50 g 1 dry cell weight [37]. This is an excellent example presenting the power of biocatalysis with respect to classical catalysis, since a simultaneous use of three different biocatalysts originated from one microorganism can be easily achieved. 

Type of enzyme (s) Ammonia lyase Hydantoinase (+ carbamoylase) Dehydrogenases Lactamase and Dehalog racemase ... 

D-phenylglycine hydantoinase/ (carbamoylase) resting cells Kanegafuchi... 

D-p-OH-phenyl- glycine hydantoinase/ carbamoylase resting cells Recordati... 

In the fine chemicals industry, enantiomerically pure amino acids are mainly produced by the aminoacylase process, the amidase process, and the hydantoinase/ carbamoylase process, all three of which are suitable for I- and D-amino acids. Dehydrogenases and transaminases are now becoming established for reduction processes. 

As evidenced by the well-established industrial production of D-amino acids (mostly D-phenylglycine and p-OH-D-phenylglycine by the hydantoinase/carbamoylase route), both D-hydantoinases and D-carbamoylases are well developed. Enantio-selectivity in most cases is not a problem (Gross, 1987). 

Fig. 31.17. Hydantoinase/Carbamoylase process for the production of D-amino acids.

The Hydantoinase-Carbamoylase System for o-Amino Acid Synthesis 5-... 

Scheme 13.13 Hydantoinase-Carbamoylase system for the deracemization of a-amino acids via DKR with in situ...

Hydantoinase-Carbamoylase System for t-Amino Acid Synthesis Despite a number of reports of strains with L-selechve hydantoin-hydrolyzing enzymes [38] the commercial application of the hydantoinase process is stiU restricted to the production of D-amino acids. Processes for the production of L-amino acids are Umited by low space-time yields and high biocatalyst costs. Recently, a new generation of an L-hydantoinase process was developed based on a tailor-made recombinant whole cell biocatalyst. Further reduction of biocatalyst cost by use of recombinant Escherichia coli cells overexpressing hydantoinase, carbamoylase, and hydantoin racemase from Arthrohacter sp. DSM 9771 were achieved. To improve the hydan-toin-converting pathway, the level of expression of the different genes was balanced on the basis of their specific activities. The system has been appUed to the preparation of L-methionine the space-time yield is however still Umited [39]. Improvements in the deracemization process from rac-5-substituted hydantoins to L-amino acids still requires a more selective L-hydantoinase. 

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