A Pseudomonas putida ATCC12633 gene, dpkA, encoding a putative protein annotated as malate/l-lactate dehydrogenase in various sequence data bases was disrupted by homologous recombination. The resultant dpkA– mutant was deprived of the ability to use d-lysine and also d-proline as a sole carbon source. The dpkA gene was cloned and overexpressed in Escherichia coli, and the gene product was characterized. The enzyme showed neither malate dehydrogenase nor lactate dehydrogenase activity but catalyzed the NADPH-dependent reduction of such cyclic imines as Δ1-piperideine-2-carboxylate and Δ1-pyrroline-2-carboxylate to form l-pipecolate and l-proline, respectively. NADH also served as a hydrogen donor for both substrates, although the reaction rates were less than 1% of those with NADPH. The reverse reactions were also catalyzed by the enzyme but at much lower rates. Thus, the enzyme has dual metabolic functions, and we named the enzyme Δ1-piperideine-2-carboxylate/Δ1-pyrroline-2-carboxylate reductase, the first member of a novel subclass in a large family of NAD(P)-dependent oxidoreductases.

Reductase Involved in the Catabolism of D-Lysine and D-Proline*

Threonine aldolase (TA)-catalyzed aldol condensation is a powerful tool for C–C bond formation under mild conditions, but the low Cβ-stereoselectivity has hampered its wide application. A stepwise ...

Improving and Inverting Cβ-Stereoselectivity of Threonine Aldolase via Substrate-Binding-Guided Mutagenesis and a Stepwise Visual Screening

We discovered a D-phenylserine deaminase that catalyzed the pyridoxal 5'-phosphate (PLP)-dependent deamination reaction from D-threo-phenylserine to phenylpyruvate in newly isolated Arthrobacter sp. TKS1. The enzyme was partially purified, and its N-terminal amino acid sequence was analyzed. Based on the sequence information, the gene encoding the enzyme was identified and expressed in Escherichia coli. The expressed protein was purified to homogeneity and characterized. The enzyme consisted of two identical 46-kDa subunits and showed maximum activity at pH 8.5 and 55°C. The enzyme was stable in the range of pH 7.5 to pH 8.5 and up to 50°C. The enzyme acted on the D-forms of β-hydroxy-α-amino acids, such as D-threo-phenylserine (K(m), 19 mM), D-serine (K(m), 5.8 mM), and D-threonine (K(m), 102 mM). As L-threonine, D-allo-threonine, L-allo-threonine, and DL-erythro-phenylserine were inert, the enzyme could distinguish D-threo-form from among the four stereoisomers of phenylserine or threonine. The enzyme was activated by ZnSO(4), CuSO(4), BaCl(2), and CoCl(2) and strongly inhibited by phenylhydrazine, sodium borohydride, hydroxylamine, and DL-penicillamine. The enzyme exhibited absorption maxima at 280 and around 415 nm. The enzyme has an N-terminal domain similar to that of alanine racemase, which belongs to the fold type III group of pyridoxal enzymes.

Discovery and characterization of D-phenylserine deaminase from Arthrobacter sp. TKS1.

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Discovery and characterization of D-phenylserine deaminase from Arthrobacter sp. TKS1.