Stereospecificity of dehydrogenases

TABLE 13-8 Stereospecificity of Dehydrogenases That Employ NAD+ or NADP+ as Coenzymes... 

A great deal of effort has been expended in trying to understand other factors that may explain the high stereospecificity of dehydrogenases.12 22 26-28... 

Fig. 6. Characteristic diamond lattice sections representing different stereospecificities of dehydrogenases [48],...

Many of the observed attributes of enzymes arise by natural selection in order to help the host organism survive and reproduce. Benner et al. have proposed that one such attribute, the stereospecificities of dehydrogenases, has functional significance based on stereochemical arguments (18, 79). The central features of their functional model can be summarized as follows. The stereospecificities of dehydrogenases acting on alcohols are correlated with the equilibrium constant for the alcohol-carbonyl redox reaction as listed in Table IV (18). Enzymes catalyzing reactions where the eq is <10 " ilf transfer the pro-S proton from NADH when is >10"" Af, the pro-R proton is transferred. Thus the more readily reduced carbonyl compounds use the pro-R proton, but the more difficult to reduce carbonyl compounds use the pro-S proton. The proposed correlation is restricted to simple aldehydes and ketones (i.e., without additional chemistry that would influence the equilibrium constant, such as cyclizations of polyols or formation of lactones). The natural substrate of the enzyme must be well... 

Table 14. Stereospecificity of dehydrogenases with respect to position 4 of the pyridine nucleus of NAD+ and NADP+...

NAD (P) " -dependent enzymes are stereospecific. Malate dehydrogenase, for example, transfers a hydride to die pro-/ position of NADH, whereas glyceraldehyde-3-phosphate dehydrogenase transfers a hydride to die pro-5 position of the nicotinamide. Alcohol dehydrogenase removes a hydride from the pro-i position of edianol and transfers it to die pro-i position of NADH. 

The stereospecificity of hydride transfer in dehydrogenases is a consequence of the asymmetric nature of die acUve site. 

The stereospecificity of hydrogen transfer for estradiol-17 and estradiol-17(3 dehydrogenases has been examined by George et a/.84>. These enzymes are both present in chicken liver, and have substrates which differ only in the chirality of their substituents at C—17. Both of these enzymes were shown to use the 4-pro-S or 4B proton of the NADPH. Since the steroid is a bulky substrate, the authors argue that the steric fit between pyridine nucleotide and steroid cannot be as important as the role played by the enzyme in directing the fit. This paper contains an interesting summary of other recent work on the stereospecificity of pyridine nucleotide dependent-steroid dehydrogenases. 

Betz, G., Warren, J. C. Reaction mechanism and stereospecificity of 20 jS-hydroxysteroid dehydrogenase. Arch. Biochem, Biophys. 128, 745—752 (1968). 

Fisher, H. F., Adija, D. L., Cross, D. G. Dehydrogenase-reduced coenzyme difference spectra, their resolution and relationship to the stereospecificity of hydrogen transfer. Biochemistry 8, 4424—4430 (1969). 

Bartoschek, S., Buurman, G., Thauer, R. K., Geierstanger, B. H., Weyrauch, J. P., Griesinger, C., Nilges, M., Hutter, M. C., Helms, V. (2001) Re-face stereospecificity of methylenetetrahy-dromethanopterin dehydrogenases and methylenetetrahydrofolate dehydrogenases is predetermined by intrinsic properties of the substrate. Chem Bio Chem, in press. 

Moinuddin SGA, Youn B, Bedgar DL et al (2006) Secoisolariciresinol dehydrogenase mode of catalysis and stereospecificity of hydride transfer in Podophyllum peltatum. Org Biol Chem 4 808-816... 

The characteristic stereospecificity of enzymes has been exploited in the design of an electrochemical cell for the conversion of L-lactate to D-lactate (Scheme 23)117. Enzymatic oxidation of L-lactate by L-lactate dehydrogenase affords pyruvate. Pyruvate is then reduced electrochemically to racemic lactate. A second enzymatic oxidation of the latter by L-lactate dehydrogenase selectively converts L-lactate to pyruvate, leaving D-lactate behind. The ingenious feature of this system is the fact that pyruvate can be re-reduced... 

C. Heiss, M. Laivenieks, G. J. Zeikus, and R. S. Phillips, The stereospecificity of secondary alcohol dehydrogenase from Thermoanaerobacter ethanolicus is partially determined by active site water,... 

Apply Microsoft Access to design a database appended with queries for retrieving groups of dehydrogenases according to their coenzyme specificity and stereospecificity. 

Reaction (1) involves a stereospecific net transfer of a hydride ion between a substrate and the C(4) of the pyridine ring of the coenzyme and an exchange of a proton with the medium 14). The generally accepted formal potential, E° of the NAD+/NADH redox couple is -560 mV vs SCE (pH 7, 25°C) 15). This value is obtained from equilibrium constants of dehydrogenase catalyzed reactions and thermal data. For most systems the equilibrium of reaction (1) favors the substrate rather than the product side. The reason for this is the low oxidizing power of NAD+, which is reflected by the low value of E° ... 

It is the spirit of the 1980s that all scientific endeavour should be useful. Finally, then, let it be recorded that the stereochemistry of dehydrogenases has important applications in biochemical analysis, in small-scale stereospecific syntheses, and in the design of therapeutic substances. 

The coenzyme stereospecificity of glyceraldehyde 3-phosphate dehydrogenase is the opposite of that of alcohol dehydrogenase... 

Exploitation of the complementary specificities of enzymes from different sources towards the same racemic substrate permits very precise control of the product stereochemistry. For example, any one of the three diastereomeric 2-decalols (94)-(96) can be obtained at will from ( )-tra/iJ-2-decalone (81 R = H) using the alcohol dehydrogenases HLADH, MJADH or CFADH, respectively (Scheme 40). The stereospecificities of these three enzymes are well documented and a simple active site model of predictive value is available for each. 55 Racemic bridged bicyclic ketones are similarly discriminated, either... 

Smithgall, T. E., Harvey, R. G., and Penning, T. M. (1986). Regio- and stereospecificity of homogeneous 3-alpha-hydroxysteroid-dihydrodiol dehydrogenase for trans-dihydrodiol metabolites of polycyclic aromatic hydrocarbons. J Biol Chem 261, 6184-6191. 

G. Raddatz, H. Bisswanger. Receptor site and stereospecifity of dihydrolipoamide dehydrogenase for R- and S-lipoamide a molecular modeling study. J Biotechnol. 1997, 58, 89-100. 

An Approach to Understanding the Stereospecificity of NAD+/NADH-Dependent Dehydrogenases, J. Am. Chem. Soc. 113, 2353-2358. 

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