Enzymes for reductions

DN 25L . [Novo Nradisk] Dextranase enzyme for reduction of dextran content in sugar juices. 

Enzyme catalyzed reductions of carbonyl groups are more often than not com pletely stereoselective Pyruvic acid for example is converted exclusively to (5) (+) lactic acid by the lactate dehydrogenase NADH system (Section 15 11) The enantiomer... 

Recent patents and pubHcations describe process improvements. Conversions can be followed by on-line hplc (93). The enzyme amidase can be used to reduce residual monomers (94—96). A hydrogenation process for reduction of acrylamide in emulsions containing more that 5% residual monomer has been patented (95). Biodegradable oils have been developed (97). 

Dinitrogen has a dissociation energy of 941 kj/mol (225 kcal/mol) and an ionisation potential of 15.6 eV. Both values indicate that it is difficult to either cleave or oxidize N2. For reduction, electrons must be added to the lowest unoccupied molecular orbital of N2 at —7 eV. This occurs only in the presence of highly electropositive metals such as lithium. However, lithium also reacts with water. Thus, such highly energetic interactions ate unlikely to occur in the aqueous environment of the natural enzymic system. Even so, highly reducing systems have achieved some success in N2 reduction even in aqueous solvents. 

The requirement for reduction prior to DNA alkylation and crosslinking was first demonstrated by Iyer and Szybalski in 1964 [29], and can be induced both by chemical reducing agents such as sodium dithionite and thiols in vitro and by various reductive enzymes such as DT-diaphorase (NAD(P)H-quinone oxidoreduc-tase) in vitro and in vivo [47]. Much work to characterize the mechanism of reductive activation and alkylation has been carried out, principally by the Tomasz and Kohn groups, and Figure 11.1 illustrates a generally accepted pathway for mitomycin C [16, 48-50] based on these experiments, which is very similar to the mechanism originally proposed by Iyer and Szybalski [29]. 

An isolated enzyme is also used for the reduction in SCCO2 [20cj. H LADH was used for reduction of butyraldehyde as shovm in Figure 8.27. In this case, addition of... 

A second theoretical inconsistency with a radical mechanism for the biochemical reaction was described by Finke. Although cleavage of the methyl-Co(II) bond is very efficient and rapid process, he argued that homolysis of methyl-Co does not occur in enzymes because reduction of CHs-Co requires too low a potential for biochemically relevant electron donors (<-1.0 V vs NHE) (195). For example, the mid-... 

For bio-transformation processes, immobilised enzymes are often used because their activity persists over a longer period of time than that of free enzymes. The reduction of enzyme activity in enzymatic reactors is a consequence of energy dissipation by sparging and stirring, which is required for instance for oxygen transport or realisation of constant reaction conditions as regards temperature and pH. In the other hand low and high pH-values leads also to a decrease of enzyme activity and increase the stress sensitivity. 

A number of peptide hormones have a carboxyl terminal amide which is derived from a glycine terminal residue. This glycine is hydroxylated on the a-carbon by a copper-containing enzyme, peptidylglycine hydroxylase, which, again, requires ascorbate for reduction of Cu ". ... 

Development of new reduction systems that reduce sterically hindered compounds The reported examples of reduction of carbonyl compounds are usually for the substrates that can be easily reduced such as methyl ketones. Since the demand for reduction of various types of compounds is increasing, investigation of new biocatalytic reductions is required. Photosynthetic organisms are not investigated yet, and they may have new type of enzymes, which can reduce sterically hindered compounds. 

Mutations in another region, the second cytoplasmic loop between M2 and M3 in Ca-ATPase of sarcoplasmic reticulum (Thr ->Ala, Gly -t Ala, and Glu Gln) also result in a complete loss of Ca-transport and Ca-ATPase activity associated with a dramatic reduction in the rate of phosphoenzyme turnover [96]. These mutations do not affect the affinity of the enzyme for Pj and therefore resemble the Pro mutants [123] in that they affect only the E1P-E2P conformational change and not the affinities for ATP, Ca or Pj. 

Although reduction of chromate Cr to Cr has been observed in a number of bacteria, these are not necessarily associated with chromate resistance. For example, reduction of chromate has been observed with cytochrome Cj in Desulfovibrio vulgaris (Lovley and Phillips 1994), soluble chromate reductase has been purified from Pseudomonas putida (Park et al. 2000), and a membrane-bound reductase has been purified from Enterobacter cloacae (Wang et al. 1990). The flavoprotein reductases from Pseudomonas putida (ChrR) and Escherichia coli (YieF) have been purified and can reduce Cr(VI) to Cr(III) (Ackerley et al. 2004). Whereas ChrR generated a semi-quinone and reactive oxygen species, YieR yielded no semiquinone, and is apparently an obligate four-electron reductant. It could therefore present a suitable enzyme for bioremediation. 

The degradation of trichloroethene by methylotrophic bacteria involves the epoxide as intermediate (Little et al. 1988). Further transformation of this may produce CO that can toxify the bacterium, both by competition for reductant and by enzyme inhibition (Henry and Grbic-Galic 1991). The inhibitory effect of CO may, however, be effectively overcome by adding a reductant such as formate. 

This similarity between MDMA and PCA is also observed in vivo in that PCA produces both an acute and long-term depletion of 5-HT (Fuller et al. 1975 Steranka et al. 1977). Like PCA, the acute decrease in 5-HT concentrations produced by MDMA is associated with a decrease in the activity of the rate-limiting enzyme for 5-HT synthesis, tryptophan hydroxylase (TPH). The timecourse of this change in cortical enzyme activity is also shown in figure 1. More detailed analysis of this acute effect of MDMA and kinetic analysis of TPH activity reveals that the decrease in enzyme activity actually precedes the decline in transmitter levels and is due to a reduction in the activity of the enzyme (Schmidt and Taylor 1987 Schmidt and Taylor 1988). As shown for the cortex in figure 3, the decrease in 5-HT... 

Intramuscular/subcutaneous for reduction in enzyme antibody effects L-Asparaginase... 

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