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The direct generation of aldehydes from carboxylic acids is often a challenging synthetic task but undoubtedly attractive in view of abundant supply of such feedstocks from nature. Though long known, biocatalytic carboxylate reductions are at an early stage of development, presumably because of their co‐factor requirement. To establish an alternative to whole‐cell‐based carboxylate reductions which are limited by side reactions, we developed an in vitro multi‐enzyme system that allows for quantitative reductions of various carboxylic acids with full recycling of all cofactors and prevention of undesired over‐reductions. Regeneration of adenosine 5′‐triphosphate is achieved through the simultaneous action of polyphosphate kinases from Meiothermus ruber and Sinorhizobium meliloti and β‐nicotinamide adenine dinucleotide 2′‐phosphate is reduced by a glucose dehydrogenase. Under these conditions and in the presence of the carboxylate reductases from Neurospora crassa or Nocardia iowensis, various aromatic, heterocyclic and aliphatic carboxylic acids were quantitatively reduced to the respective aldehydes. [ABSTRACT FROM AUTHOR]

Nitrile reductase QueF catalyzes the reduction of 2-amino-5-cyanopyrrolo[2,3- d]pyrimidin-4-one (preQ0) to 2-amino-5-aminomethylpyrrolo[2,3- d]pyrimidin-4-one (preQ1) in the biosynthetic pathway of the hypermodified nucleoside queuosine. It is the only enzyme known to catalyze a reduction of a nitrile to its corresponding primary amine and could therefore expand the toolbox of biocatalytic reactions of nitriles. To evaluate this new oxidoreductase for application in biocatalytic reactions, investigation of its substrate scope is prerequisite. We report here an investigation of the active site binding properties and the substrate scope of nitrile reductase QueF from Escherichia coli. Screenings with simple nitrile structures revealed high substrate specificity. Consequently, binding interactions of the substrate to the active site were identified based on a new homology model of E. coli QueF and modeled complex structures of the natural and non-natural substrates. Various structural analogues of the natural substrate preQ0 were synthesized and screened with wild-type QueF from E. coli and several active site mutants. Two amino acid residues Cys190 and Asp197 were shown to play an essential role in the catalytic mechanism. Three non-natural substrates were identified and compared to the natural substrate regarding their specific activities by using wild-type and mutant nitrile reductase. [ABSTRACT FROM AUTHOR]

Nitrile reductase QueF catalyzes the reduction of a nitrile to its corresponding amine. In their Full Paper on page 7007 ff., N. Klempier et al. report on the investigation of active‐site binding and the substrate scope of E. coli QueF by modeling, enzyme, and substrate engineering. The active‐site residues and structural features of the substrates essential for catalysis were identified in spectrophotometric and HPLC‐MS based screenings of active‐site mutants and natural substrate analogues. [ABSTRACT FROM AUTHOR]