Catalytic activity, enzymes carbohydrate synthesis

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-... 

Morales. J.C. Zurita. D. Penades. S. Carbohydrate-carbohydrate interactions in water with glycophanes as model systems. J. Org. Chern. 1998. 63. 9212-9222. Habicher. T. Diederich, F. Catalytic dendrophanes as enzyme mimics Synthesis, binding properties, micropolarity effect, and catalytic activity of dendritic thiazolio-cyclophanes. Helv. Chim. Acta 1999. 82, 1066-1094. Bartsch, R.A. Kus, P. Dailey, N.K. Kou. X. A novel cyclophane-anthracene complex. Tetrahedron Lett. 2002. 43. 5017-5019. 

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