Enantioselective reduction of β,χ-unsaturated α-keto acids usingbacillus stearothermophilus lactate dehydrogenase: A new route to functionalised allylic alcohols

Attempting to remove the substrate inhibition of L-lactate dehydrogenase from Bacillus stearothermophilus by site-directed mutagenesis

L-lactate dehydrogenase (LDH) catalyzes the interconversion of an oxoacid (pyruvate) and hydroxy-acid (lactate) using the NADH/NAD+ pair as a redox cofactor. The enzyme has a commercial significance, as it can be used to produce chiral building blocks for the synthesis of key pharmaceuticals and agrochemicals. However, the substrate inhibition which is due to an abortive NAD+-pyruvate complex reducing the steady state concentration of functional LDH limits its use in industry. This substrate inhibition can be overcome by weaking the binding of NAD+. The conserved aspartic acid residue at position 38 was replaced by the longer basic arginine side chain (D38R) using PCR based overlap extension mutagenesis technique in the hope of weakening NAD+-binding. The mutant gene was overexpressed in the Escherichia coli high-expression vector pKK223-3 in JM105 cells; then, the mutant protein was produced. Comparing the effect of substrate inhibition in the arginine-38 mutant with wild-type, substrate inhibition is decreased threefold.

Epoxide hydrolases and their synthetic applications

Chiral epoxides and 1,2-diols, which are central building blocks for the asymmetric synthesis of bioactive compounds, can be obtained by using enzymes--i.e. epoxide hydrolases--which catalyse the enantioselective hydrolysis of epoxides. These biocatalysis have recently been found to be more widely distributed in fungi and bacteria than previously expected. Sufficient sources from bacteria, such as Rhodococcus and Nocardia spp., or fungi, as for instance Aspergillus and Beauveria spp., have now been identified. The reaction proceeds via an SN2-specific opening of the epoxide, leading to the formation of the corresponding trans-configured 1,2-diol. For the resolution of racemic monosubstituted and 2,2- or 2,3-disubstituted substrates, various fungi and bacteria have been shown to possess excellent enantioselectivities. Additionally, different methods, which lead to the formation of the optically pure product diol in a chemical yield far beyond the 50% mark (which is intrinsic to classic kinetic resolutions), are discussed. In addition, the use of non-natural nucleophiles such as azides or amines provides access to enantiomerically enriched vicinal azido- and amino-alcohols. The synthetic potential of these enzymes for asymmetric synthesis is illustrated with recent examples, describing the preparation of some biologically active molecules.

Purification of carp (Cyprinus carpio) hepatopancreatic lactate dehydrogenase (EC 1.1.1.27)

Lactate dehydrogenase (LDH, EC 1.1.1.27) was isolated in 86% purity from carp (Cyprinus carpio) hepatopancreas using agarose T-gel (mercaptoethanol bound to agarose via divinylsulphone) affinity chromatography medium and Iontosorb phenyl hydrophobic chromatography medium. Gel filtration chromatography of the LDH obtained shows molecular weight to be 26,900 Da.