Reduction hyperthermophilic enzymes

The pharmaceutical and fine chemical industry might use pure hydrogenase or partially purified enzyme preparations in bioconversion applications such as regio and stereoselective hydrogenation of target compounds (van Berkel-Arts et al. 1986). Enzymes are able to catalyse such stereospecific syntheses with ease. However, the cofactors for the NAD-dependent oxidoreductases are expensive. The pyridine nucleotide-dependent hydrogenases such as those from Ralstonia eutropha and hyperthermophilic archaea (Rakhely et al. 1999) make it possible to exploit H2 as a low-cost reductant. The use of inverted micelles in hydrophobic solvents, in which H2 is soluble, has advantages in that the enzymes appear to be stabilized. 

Figure lO.lOA shows the reaction scheme of the system outlining the electron transfer pathway among the different components, namely the electron donor Tris, the semiconductor Ti02 and the sulfhydrogenase of the hyperthermophilic archaeon P. furtosus, a bifunctional enzyme catalysing either proton or sulfur species reduction. 

A recent detailed characterization of the putative CoADR enzyme from Pyrococcus furiosus have shown that this protein is in fact a CoA-dependent NAD(P)H elemental sulfur oxidoreductase (NSR), which is mainly involved in the reduction of S° to H2S in this heterotrophic hyperthermophile. Previous studies of the... 

A two-enzyme process to obtain alcohols from carboxylic adds was reported by Ni et al. as shown in Scheme 6.32. The reduction of the add moiety was demonstrated by the hyperthermophile Pyrococcus furiosus using 5 bar of hydrogen as re-ductant. It was also shown that no reaction occurred in the absence of P. furiosus or hydrogen. Both aromatic and aliphatic substrates were used and reduction of the carboxylic add resulted in the accumulation of aldehyde intermediate. The aldehyde was reduced using a CRED with overall yields of 11-99% [47]. 

---