Mechanism of Asymmetric Production of l-Aromatic Amino Acids from the Corresponding Hydantoins by Flavobacterium sp.

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Abstract
The mechanism of asymmetric production of l-aroniatic amino acids from the corresponding hydantoins by Flavobacterium sp. AJ-3912 was examined by investigating the properties of the enzymes involved in the hydrolysis of 5-substituted hydantoins corresponding to aromatic amino acids (A AH). The enzymatic hydrolysis of AAH by Flavobacterium sp. AJ-3912 consisted of the following two successive reactions; a hydrolytic ring opening reaction of dl-AAH to l- and d-form N-carbamyl aromatic amino acids (NCA), involving an enzyme (hydantoin hydrolase), followed by a hydrolytic cleaving reaction of the l-form NCA to l-aromatic amino acids involving another enzyme (N-carbamyl-l-aromatic amino acid hydrolase, abbreviated as l-NCA hydrolase). The ring opening reaction involving hydantoin hydrolase was not stereospecific, but the NCA cleaving reaction involving l-NCA hydrolase was completely l-specific. The pathway for the conversion of the by-produced d-form NCA to l-aromatic amino acids was as follows; conversion of d-form NCA to d-AAH through the reverse reaction of hydantoin hydrolase, and then conversion of the d- AAH to l-AAH through spontaneous racemization, followed by the successive hydrolysis of the l- AAH to l-aromatic amino acids by hydantoin hydrolase and l-NCA hydrolase.