Dehydrogenases formate dehydrogenase

Reductive acetyl-CoA pathway 4-5 3 NAD(P)H, 2-3 ferredoxin, 1 H2 (in methanogens) Acetyl-CoA synthase/ CO dehydrogenase, formate dehydrogenase, pyruvate synthase C02 Acetyl-CoA, pyruvate Acetyl-CoA synthase/CO dehydrogenase, enzymes reducing C02 to methyltetrahydropterin... 

Table 17-2. Synthesis of D-amino acids from a-keto acids by combination of four purified enzymes alanine racemase, L-alanine dehydrogenase, formate dehydrogenase, and D-amino acid aminotransferase.

Aldehyde oxidoreductase (dehydrogenase) Formate dehydrogenase CO dehydrogenase (oxidoreductase)... 

Alcohol dehydrogenase (5) and leucine a-ketoglutarate transaminase (33,34) contribute to the development of aroma during black tea manufacturing. Polyphenol oxidase and peroxidase are essential to the formation of polyphenols unique to fermented teas. 

KA Gray, VL Davidson, DB Knaff. Complex formation between methylamine dehydrogenase and amicyanm from Paracocuus demtnficans. J Biol Chem 263 13987-13990, 1988. 

FIGURE 16.10 Formation of a covalent intermediate in the glyceraldehyde-3-phos-phate dehydrogenase reaction. Nucleophilic attack by a cysteine —SH group forms a covalent acylcysteine intermediate. Following hydride transfer to NAD, nucleophilic attack by phosphate yields the product, 1,3-bisphosphoglycerate. 

Ketone body synthesis occurs only in the mitochondrial matrix. The reactions responsible for the formation of ketone bodies are shown in Figure 24.28. The first reaction—the condensation of two molecules of acetyl-CoA to form acetoacetyl-CoA—is catalyzed by thiolase, which is also known as acetoacetyl-CoA thiolase or acetyl-CoA acetyltransferase. This is the same enzyme that carries out the thiolase reaction in /3-oxidation, but here it runs in reverse. The second reaction adds another molecule of acetyl-CoA to give (i-hydroxy-(i-methyl-glutaryl-CoA, commonly abbreviated HMG-CoA. These two mitochondrial matrix reactions are analogous to the first two steps in cholesterol biosynthesis, a cytosolic process, as we shall see in Chapter 25. HMG-CoA is converted to acetoacetate and acetyl-CoA by the action of HMG-CoA lyase in a mixed aldol-Claisen ester cleavage reaction. This reaction is mechanistically similar to the reverse of the citrate synthase reaction in the TCA cycle. A membrane-bound enzyme, /3-hydroxybutyrate dehydrogenase, then can reduce acetoacetate to /3-hydroxybutyrate. 

In order to broaden the field of biocatalysis in ionic liquids, other enzyme classes have also been screened. Of special interest are oxidoreductases for the enan-tioselective reduction of prochiral ketones [40]. Formate dehydrogenase from Candida boidinii was found to be stable and active in mixtures of [MMIM][MeS04] with buffer (Entry 12) [41]. So far, however, we have not been able to find an alcohol dehydrogenase that is active in the presence of ionic liquids in order to make use of another advantage of ionic liquids that they increase the solubility of hydrophobic compounds in aqueous systems. On addition of 40 % v/v of [MMIM][MeS04] to water, for example, the solubility of acetophenone is increased from 20 mmol to 200 mmol L ... 

The diagram looks very promising in terms of citric acid formation in that a-oxoglutarate dehydrogenase is inactive, isodtrate dehydrogenase has veiy low activity and aconitase equilibrates 90% towards dtric add. 

Formamidine, N,N -di-2-anthraquinonyI-metal complexes, 2,275 Formamidine, IV.AT-diaryl-metal complexes, 2, 275 Formamidine, N, N -dibenzyl-metal complexes, 2,276 Formamidine, IV.N -diisopropyl-metal complexes, 2, 276 Formamidinesulfinic acid technetium complexes, 6, 974 Formate dehydrogenases bacteria... 

Alcohols such as ethanol, 2-propanol, and so on, have been widely used to recycle the coenzyme for the reduction catalyzed by alcohol dehydrogenase since the enzyme catalyzes both reduction and oxidation. Usually, an excess amount of the hydrogen source is used to push the equilibrium toward formation of product alcohols. 

Figure 8.3 Reduction of ketone with alcohol dehydrogenase from Rhodococcus erythropolis using formate as a hydrogen source [4a].

Figure 8.8 Reduction of carbon dioxide with formate dehydrogenase and porphyrin complex using light energy [6h].

---