Dehydrogenases coenzyme specificity

Transfer of hydrogen from one substrate to another in a coupled oxidation-reduction reaction (Figure 11-3). These dehydrogenases are specific for their substrates but often utilize common coenzymes or hydrogen carriers, eg, NAD". Since the reactions are re-... 

Complex II. The succinate dehydrogenase complex, or complex IF, contains a non-haem iron-sulfur component and utilises the electron acceptor FAD to effect the transfer of electrons from FADH2 to coenzyme Q. Inhibitors of succinate dehydrogenase are specific basidio-mycete fungicides, with uses against smuts, bunts, and Rhizoctonia spp. (Figure 4.21). 

They stated further that, the new adaptive enzyme catalyzing Reaction 3 appears to be similar to the malic enzyme of pigeon liver, although strictly DPN (instead of TPN)-specific. The coenzyme specificity explains the ready occurrence of Reaction 1. Therefore, the authors showed that exogenous NAD was required for the overall reaction (malic acid -> lactic acid), but because this activity was measured manometrically, they never demonstrated the formation of reduced NAD. Similarly, they did not attempt to show that pyruvic acid was the intermediate between L-malic acid and lactic acid. Instead, the formation of pyruvic acid was inferred from the NAD requirement and because the malic acid dissimilation activity remained constant during purification while the lactate dehydrogenase activity decreased (14). In fact, attempts to show any appreciable amounts of pyruvic acid intermediate failed (22). 

The dehydrogenases discussed in this section catalyze the oxidation of alcohols to carbonyl compounds. They utilize either NAD+ or NADP+ as coenzymes. The complex of the enzyme and coenzyme is termed the holoenzyme the free enzyme is called the apotnzyme. Some dehydrogenases are specific for just one of the coenzymes a few use both. The reactions are readily reversible, so that carbonyl compounds may be reduced by NADH or NADPH. The rates of reaction in either direction are conveniently measured by the appearance or disappearance of the reduced coenzyme, since it has a characteristic ultraviolet absorbance at 340 nm. The reduced coenzymes also fluoresce when they are excited at 340 nm, which provides an even more sensitive means of assay. 

N. Holmberg, U. Ryde, and L.Bulow, Redesign of the coenzyme specificity in L-lactate dehydrogenase from Bacillus stearothermophilus using site-directed mutagenesis and media engineering,... 

T. Yaoi, K. Miyazaki, T. Oshima, Y. Komukai, and M. Go, Conversion of the coenzyme specificity of isodtrate dehydrogenase by module replacement, J. Biochem. (Tokyo) 1996, 119, 1014-1018. 

RD Chen, A Greer, JM Hurley, AM Dean. Engineering secondary structure to invert coenzyme specificity in isopropylmalate dehydrogenase. In DR Marshak, ed. Techniques in Protein Chemistry VIII. New York Academic Press, 1997, pp 809-816. 

RD Chen, AF Greer, AM Dean. A highly active decarboxylating dehydrogenase with rationally inverted coenzyme specificity. Proc Natl Acad Sci (USA) 92 11666-11670, 1995. 

RD Chen, A Greer, AD Dean. Structural constraints in protein engineering the coenzyme specificity of Escherichia coli isocitrate dehydrogenase. Eur J Biochem 250 578-582, 1997. 

Enzymes are highly selective of the substrates with which they interact and in the reactions that they catalyze. This selective nature of enzymes collectively known as enzyme specificity can be best illustrated with oxidoreductases (dehydrogenases), which display substrate and bond specificities (e.g., acting on —CHOH—, versus —CHO versus —CH—CH— versus —CHNH2, and cis versus trans for unsaturated substrates), coenzyme specificity (e.g., NAD(H) versus NADP(H)), chiral stereospecificity (d- versus l- or R- versus S-stereoisomers), and prochiral stereospecificity (A versus B corresponding to proR- versus proS isomers and re face versus si face, respectively). The table lists some dehydrogenases and their coenzyme, substrate, product and stereospecificities (You, 1982) ... 

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

Engineering Secondary Structure to Invert Coenzyme Specificity in Isopropylmalate Dehydrogenase... 

M. Nishiyama, J. J. Birktoft, T. Beppu, Alteration of coenzyme specificity of malate dehydrogenase from Thermus flavus by site-directed mutagenesis, J. Bid. Chem. 1993, 268(7), 4656-4660. 

R. Chen, A. Greer, A. M. Dean, Redesigning secondary structure to invert coenzyme specificity in isopropylmalate dehydrogenase, Proc. Natl. Acad. Sci. USA, 1996, 93(22), 12171-12176. 

Change in the Coenzyme Specificity by Genetic Methods NADP(H) Specific Formate Dehydrogenase... 

There are at least three types of glutamate dehydrogenases which differ in coenzyme specificity those specific for either NAD or NADP and those that can function with both. For brevity, the first two will be abbre-... 

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