Hydroxyisocaproate dehydrogenase

Enzyme-catalyzed syntheses of enantiomeric pure hydroxy acids use lactate dehydrogenases (LDH E.C. 1.1.1.27) or hydroxyisocaproate dehydrogenases (HicDH). Both kinds of enzymes are available as D- or L-specific catalysts. L-specific [5, 6] LDHs as well as D-specific [7-10] LDHs favorably catalyze the reduction of pyruvate, HicDHs (and mandelate dehydrogenase, too) convert keto acids with longer aliphatic or aromatic side chains. These enzymes can be isolated from Lactobacillus strains [11-14]. 

Commercially available C. boidinii-FDH was used to recycle the NADH cofactor in stereospecific reductions by (/ )-2-hydroxyisocaproate dehydrogenase from L. casei [174]. Enantiomerically pure (R)-2-hydroxy-4-methylpentanoic acid was obtained with 88% yield. The broad substrate specificity of this enzyme enables the synthesis of a broad range of enantiomerically pure ot-hydroxy acids with aliphatic or aromatic side chains. 

Mandelic acid Benzoylformic acid Hydroxyisocaproate dehydrogenase... 

The reaction is catalyzed by D-hydroxyisocaproate dehydrogenase (D-HicDH). The essential cofactor PEG-NADH is regenerated from PEG-NAD+ by a second enzyme, formate dehydrogenase (FDH). By coupling to water-soluble polyethyleneglycol with a molar mass of 20 000 g mol-1, the cofactor can be retained, together with the enzymes, by an ultrafiltration membrane, and the whole process may be performed continuously in an enzyme membrane reactor. 

FDH, Formate dehydrogenase L-HicDH, L-Hydroxyisocaproate dehydrogenase LeuDH, Leucine dehydrogenase PheDH, Phenylalanine dehydrogenase. 

DL-phenyllactic acid + NH D- and L-hydroxyisocaproate dehydrogenase + Phe dehydrogenase Eactobacillus casei ... 

Schustolla D, Deckwer WD, Schiigerl K et al. (1992) Enzyme purification by immobilized metal ion affinity partitioning — application to D-hydroxyisocaproate dehydrogenase. Bioseparation 3(2-3) 167-175... 

Hummel W, Schiitte H, Kula MR (1985) D-2-Hydroxyisocaproate dehydrogenase from Lactobacillus casei. A new enzyme suitable for stereospedfic reduction of 2-ketocarboxylic acids. Appl Microbiol Biotechnol 21 7-15... 

There are two lactate dehydrogenases (LdHs) with different stereospecificities that have been very useful for the preparation of chiral 2-hydroxy acids.33 4 L-LdH (E.C. 1.1.1.27) and D-LdH (E.C. 1.1.1.28) are obtained from various microbial sources (Table 19.1). Along with hydroxyisocaproate... 

Selected Substrates and Stereochemical Product Configuration with Lactate (L) and Hydroxyisocaproate (Hie) Dehydrogenases (dH) from Various Sources that Catalyze the Reaction Shown in Scheme 19.2... 

L. Lactis (84 strains) AA converting activity (cell extracts from cells grown in 2 media) Activity of branched chain aminotransferase (BcaT), alpha-hydroxyisocaproic acid dehydrogenase (HicDH), and esterase individual strains showed va-y diverse regulatory responses, with the activities in the 2 media in general poorly correlated (Bachmann et al. 2009)... 

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