Optimal Reaction Condotions for the Enzymatic Synthesis of Optically Active D-p-Hydroxyphenylglycine from 5-substituted Hydantoin Using D-Hydantoinase and N-Carbamoylase
Geun-Joong Kim and Hak-Sung Kim
Currently, D-amino acids are commercially produced from DL-5-substituted hydantoin using D-specific hydantoinase. In this process, chemically synthesized DL-5-substituted hydantoin is asymmetrically hydrolyzed to N-carbamoyl-D-amino acid using D-hydantoinase, and this compound is further chemically converted to the corresponding D-amino acid. However, chemical hydrolysis of N-carbamoyl-D-amino acid under an acidic condition needs an additional unit operation and might generate a large amount of process waste. Treatment of waste is becoming one of the most sognificant factors to be considered in the process developmeent. Accordingly, from a practical standpoint, enzymatic hydrolysis of N-carbamoyl-D-amino acid will be economically favorable because the process becomes simple, and waste discharge could be minimized.Until now, several microorganisms possessing both D-hydantoinase and N-carbamoylase were isolated, and optimal conditions and kinetic aspects regarding one-step conversion of DL-5-substituted hydantoin to the corresponding D-amino acid have been intensively investigated. However, N-carbamoylase has not been employed in a commercial process due to low activity compared that of D-hydantoinase.In this work, we attempt to optimize the reaction conditions that are basically required to develop the process for the direct enzymatic production of D-p-hydroxyphenylglycine(D-HPG) from DL-5-substituted hydantoin using D-hydantoinase and N-carbamoylase of Agrobacterium sp. I-671.