- Characterization of three novel enzymes with imine reductase activity
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Imine reductases (IRED) are promising catalysts for the synthesis of optically pure secondary cyclic amines. Three novel IREDs from Paenibacillus elgii B69, Streptomyces ipomoeae 91-03 and Pseudomonas putida KT2440 were identified by amino acid or structural similarity search, cloned and recombinantly expressed in E. coli and their substrate scope was investigated. Besides the acceptance of cyclic amines, also acyclic amines could be identified as substrates for all IREDs. For the IRED from P. putida, a crystal structure (PDB-code 3L6D) is available in the database, but the function of the protein was not investigated so far. This enzyme showed the highest apparent E-value of approximately Eapp = 52 for (R)-methylpyrrolidine of the IREDs investigated in this study. Thus, an excellent enantiomeric purity of >99% and 97% conversion was reached in a biocatalytic reaction using resting cells after 24 h. Interestingly, a histidine residue could be confirmed as a catalytic residue by mutagenesis, but the residue is placed one turn aside compared to the formally known position of the catalytic Asp187 of Streptomyces kanamyceticus IRED.
- Gand,Müller,Wardenga,H?hne
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p. 126 - 132
(2015/02/19)
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- Enzymatic synthesis of cyclic amino acids by N-methyl-l-amino acid dehydrogenase from Pseudomonas putida
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A new enzymatic system for the synthesis of enantiomerically pure cyclic amino acids (CAA) from the corresponding diamino acids or racemic CAA is described. α,ω-Diamino acids were oxidized to α-keto acids with amino acid oxidases (AAO). The α-keto acids were spontaneously transformed into cyclic imino acids in the reaction medium. The resulting imines were reduced to the l-form CAA with N-methyl-l-amino acid dehydrogenase (NMAADH) from Pseudomonas putida ATCC12633 using NADPH as a cofactor. l-Form CAA were also obtained from racemic CAA using d-amino-acid oxidase and NMAADH. Using this method, a new compound [1,4]-thiazepane-3-carboxylic acid (Fig. 1) was synthesized from aminopropylcystein.
- Yasuda, Mari,Ueda, Makoto,Muramatsu, Hisashi,Mihara, Hisaaki,Esaki, Nobuyoshi
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p. 1775 - 1779
(2007/10/03)
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- Deuterium Isotope Effects for the Nonenzymatic and Glutamate Dehydrogenase Catalyzed Reduction of an α-Imino Acid by NADH
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The mechanisms of the nonenzymatic and glutamate dehydrogenase catalyzed reduction of an α-imino acid, Δ1-pyrroline-2-carboxylic acid, by NAD(P)H have been studied by deuterium isotope effects.The partition isotope effects for the nonenzymatic reaction with 4-deuterated 1,4-dihydronicotinamides are about the same as the corresponding observed kinetic isotope effects with 4,4-dideuterio-1,4-dihydronicotinamides, suggesting that the hydrogen-transfer step is solely rate limiting.This reaction is characterized by an intrinsic primary kinetic isotope effect of 1.3 and a very product-like transition state.The enzymatic reaction has been studied by determining the second-order rate constants for the reduction of the imino acid by the enzyme-NADH complex with 4,4-dideuterio and stereospecifically labeled 4-deuterio NADH.The primary isotope effect when the in-place hydrogen is protium is 3.80, and the secondary isotope effect when the in-flight hydrogen is protium is 1.21.Deuteration at one site lowers the isotope effects at the other by 13percent.The following conclusions emerge for the reduction of the imino acid by the enzyme-NADH complex: (1) the hydrogen-transfer step is at least rate contributing, (2) the transition state for this reaction is more symmetric than that of the nonenzymatic reaction, (3) both the C-4 hydrogens of NADH participate in the reaction coordinate motion, and (4) there is some nuclear tunneling in the reaction coordinate.The kinetic isotope effect for the oxidation of proline and proline-2-d by enzyme-NADP(+) is 4.1.
- Srinivasan, R.,Fisher, Harvey F.
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p. 4301 - 4305
(2007/10/02)
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- Conversion of ω-Guanidino- and ω-Ureido-α-amino Acids into α-Keto Acids and Heterocycles Derived Therefrom
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Treatment of basic α-amino acids 1 with trifluoroacetic anhydride readily leads to 2-trifluoromethyl-3-oxazolin-5-ones 2, which in turn may be hydrolyzed to yield α-keto acids 4 under mild conditions.Type 4 compounds carrying ω-guanidino or ω-ureido funct
- Klein, Christian,Schulz, Guenter,Steglich, Wolfgang
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p. 1623 - 1637
(2007/10/02)
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