Enzymatic reaction has increasingly been applied to organic synthesis (1-3), and there are several reports of the attempted in vitro synthesis of the D-amino acid-containing peptides and amides (4-10). However, because these enzymatic reactions are not stereospecific for substrates with D-configurations, they are at an innate disadvantage. Some peptidases and amidases act on peptides and amides containing D-amino acids. Soluble Streptomyces carboxy-peptidase DD catalyzes not only the transpeptidation reaction on the peptide intermediate in peptidoglycan biosynthesis but also the hydrolysis of Aa,Ae-diacetyl-L-lysyl-(D-Ala) 2 in water (11). A D-peptidase has been purified and characterized from an actinomycete, although it is not strictly specific toward peptides containing D-amino acids (12). In Enterococcus, the vanXgene product (D-Ala)2 hydrolase plays a role in vancomycin resistance (13). The chemically synthesized D-enzyme of an HIV-1, in which all the amino acids were replaced with the corresponding D-amino acids, displays D-stereospecificity (14). D-Stereospe-cific amino acid amidases (amidohydrolases) were isolated from some microorganisms (15-17). Of the enzymes, a D-alaninamide-specific amidohydrolase from Arthrobacter has been used in the industrial manufacture of D- and L-alanine (17,18). Production of D-amino acids by use of Dor L-specific enzymes such as D-amino acylase, D-hydan-toin hydrolase, A-carbamoyl-D-amino acid hydrolase, D-amidase, D-transaminase, and amino acid racemase was recently reviewed (19,20).

A new enzyme, D-aminopeptidase, was isolated from Ochrobactrum anthropi and characterized. We describe its

Time (min)

Figure 1. Kinetic resolution of dl-alanine amide by O. anthropi d-aminopeptidase. A reaction mixture containing 0.5 mmol tris(hydrochloride), pH 8.0, 0.1 mmol dl-alanine amide hydrochloride, and 5 units of the purified enzyme in a total volume of 5.0 mL was incubated at 30 °C. The content of l-alanine was measured by l-alanine dehydrogenase.

Table 1. Substrate Specificity of D-Aminopeptidase from O. anthropi SCRC C1-38

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