CITRIC ACID CYCLE`S PROBLEM

Diposting oleh uZaMi hAmZah
Senin, 06 Juni 2011

Which of following reaction do not produce the NADH as adding product at Krebs Circle?
a. Isocytrate → Oxalosuccinate
b. Alpha ketoglutarate → succinate
c. Succinate → Fumarate
d. Malate → Oxaloacetat



1. Formation of Citrate The first reaction of the cycle isthe condensation of acetyl-CoA with oxaloacetate to form citrate, catalyzed by citrate synthase
2 Formation of Isocitrate via cis-Aconitate The enzyme aconitase (more formally, aconitate hydratase) catalyzes the reversible transformation of citrate to isocitrate, through the intermediary formation of the tricarboxylic acid cis-aconitate, which normally does not dissociate from the active site. Aconitase can promote the reversible addition of H2O to the double bond of enzyme-bound cis-aconitate in two different ways,
one leading to citrate and the other to isocitrate
3 Oxidation of Isocitrate to alpha-Ketoglutarate and CO2 In the next step, isocitrate dehydrogenase catalyzes oxidative decarboxylation of isocitrate to form alpha ketoglutarateThere are two different forms of isocitrate dehydrogenasein all cells, one requiring NAD_ as electron acceptor and the other requiring NADP_. The overall reactions are otherwise identical. In eukaryotic cells, the NAD-dependent enzyme occurs in the mitochondrial matrix and serves in the citric acid cycle. The main function mitochondrial matrix and the cytosol, may be the generation of NADPH, which is essential for reductive anabolic reactions.
4 Oxidation of _-Ketoglutarate to Succinyl-CoA and CO2 The next step is another oxidative decarboxylation, in which _-ketoglutarate is converted to succinyl-CoA and CO2 by the action of the _-ketoglutarate dehydrogenase complex; NAD_ serves as electron acceptor
and CoA as the carrier of the succinyl group. The energy of oxidation of _-ketoglutarate is conserved in the formation of the thioester bond of succinyl-CoA
5 Conversion of Succinyl-CoA to Succinate Succinyl-CoA, like acetyl-CoA, has a thioester bond with a strongly negative standard free energy of hydrolysis
6. At the 5th step Reaction at Krebs Circle, succinate is oxidized by enzyme Succinate dehydrogenase that bond with FAD as co-enzyme. This enzyme bonded strongly at mitochondrion. In this Reaction FAD as acceptor of hydrogen and produce FADH2
7 Hydration of Fumarate to Malate The reversible hydration of fumarate to L-malate is catalyzed by fumarase
8 Oxidation of Malate to Oxaloacetate In the last reaction of the citric acid cycle, NAD-linked L-malate dehydrogenase catalyzes the oxidation of L-malate to oxaloacetate


REFERENCES
Lehninger. Principle of Biochemistry 4th edition.

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