Effect of cell membrane of Agrobacterium radiobacter on enhancing D-amino acids production from racemic hydantoins

An interesting phenomenon was observed that the existence of the intact cell membrane can enhance the D-amino acids production from D,L-5-substituted hydantoins by reacting with the whole cells of Agrobacterium radiobacter. Two intracellular enzymes were involved in the reaction process. The first enzyme D-hydantoinase converted hydantoins to carbamoyl derivatives which were further converted to D-amino acids by D-amidohydrolase. The amount of D-amino acids produced from hydantoins by the intact cells were 1.8–2.4 fold higher than the toluene treated cells. In addition, by using the intact cells the amount of D-amino acids produced from hydantoins was about 10 fold higher than that produced directly from carbamoyl derivatives. The relatively lower permeability of cell membrane to the reaction intermediate carbamoyl derivatives was confirmed by a simple mathematical model to be the main factor for the better performance of the intact cells for D-amino acid production. Besides, the low intracellular enzymes activities also contributed to the effect of intact cell membrane on enhancing the D-amino acid production.