Reversible electron transfer, fructose

A reversible covalent modification that plants use extensively is the reduction of cystine disulfide bridges to sulf-hydryls. Many of the enzymes of photosynthetic carbohydrate synthesis are activated in this way (table 9.3). Some of the enzymes of carbohydrate breakdown are inactivated by the same mechanism. The reductant is a small protein called thioredoxin, which undergoes a complementary oxidation of cysteine residues to cystine (fig. 9.5). Thioredoxin itself is reduced by electron-transfer reactions driven by sunlight, which serves as a signal to switch carbohydrate metabolism from carbohydrate breakdown to synthesis. In one of the regulated enzymes, phosphoribulokinase, one of the freed cysteines probably forms part of the catalytic active site. In nicotinamide-adenine dinucleotide phosphate (NADP)-malate dehydrogenase and fructose-1,6-bis-... 

Electronic communication of fructose dehydrogenase (FDH) with a Pt electrode was accomplished through the conducting polymer molecular interface. Electrons were reversibly transferred between the active center of FDH and the electrode surface when the electrode potential was properly controlled. The enzyme activity of the molecular-interfaced FDH was found to be modulated in the presence of D-fructose by the electrode potential. Electronic communication of alcohol dehydrogenase (ADH) with a Pt electrode was also accomplished in the... 

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