Acylamino acid racemase

M.-R. Kula, Screening, overexpression and characterization of an N-acylamino acid racemase from Amycolatopsis orientalis subsp. lurida, Appl. Microbiol. Biotechnol. 2001, 55, 354-361. 

A method that has been used to approach 100% theoretical yield in asymmetric syntheses is dynamic kinetic resolution, or DKR. Although this method has been practiced based on strictly chemical reactions, only those chemoenzymatic DKR reactions will be discussed here. Most often, the enzyme used by this method is a hydrolase (lipase, esterase, protease), but other enzymes such as hydantoinases, /V-acylamino acid racemases, and dehydrogenases have also been exploited to effectively carry out DKR reactions.196 For additional details the reader is directed to the many review articles written on DKR.197 206... 

Takahashi and Hatano of Takeda Chemical Industries, Japan, succeeded in finding a racemase that acts on N-acylamino acids, but not on the corresponding free amino acids, and named it acylamino acid racemase1171. They have established a method of producing optically active a-amino acids from the corresponding D,L-N-acylamino acids by means of the acylamino acid racemase and aminoacylases. 

Tokuyama et al.11721 found that most of acylamino acid racemase-producing strains produce not only acylamino acid racemase but also aminoacylases one of either d- or L-aminoacylase or both of them. Moreover, acylamino acid racemase shows the optimum pH at around 8.0, which is close to that of aminoacylases. Therefore, N-acylamino acid can be converted as a whole into l- or D-amino acids in one step by means of microbial cells of appropriate strains producing either l- or D-aminoacylase in addition to acylamino acid racemase. 

The acylase-catalyzed resolution of /V-acetyl-DL-amino acids is a key commercial process. The racemization of the remaining /V-acetyl-D-amino acid after separation of the L-amino acid must be performed, but adds complexity and cost. Therefore, in situ racemization with a racemase possessing specificity for N-acylamino acids without affecting the stereochemistry of the product L-amino acids is very desirable. The pentameric enzyme from Streptomyces sp. Y-53 specifically catalyzes the racemization of N-acylamino acids without acting on amino acids [182],... 

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