Isocitrate glucose oxidation

Oxidation of reduced pyridine nucleotides Reaction with isocitrate dehydrogenase, glucose 6-phosphate dehydrogenase, malate dehydrogenase Reaction with GSH... 

It is important to note that animals are unable to effect the net synthesis of glucose from fatty acids. Specifically, acetyl CoA cannot be converted into pyruvate or oxaloacetate in animals. The two carbon atoms of the acetyl group of acetyl CoA enter the citric acid cycle, but two carbon atoms leave the cycle in the decarboxylations catalyzed by isocitrate dehydrogenase and a-ketoglutarate dehydrogenase. Consequently, oxaloacetate is regenerated, but it is not formed de novo when the acetyl unit of acetyl CoA is oxidized by the citric acid cycle. In contrast, plants have two additional enzymes enabling them to convert the carbon atoms of acetyl CoA into oxaloacetate (Section 17.4.). 

A pathway by which acetate and acetoacetate are oxidized is indicated in Fig. 8. The similarity to the mechanism of oxidation of pyruvate is striking. According to this proposed scheme acetate and acetoacetate are converted to a hypothetical two-carbon intermediate which is capable of condensing with oxalacetate or one of the other four-carbon dicarboxylic acids to yield cis-aconitate or isocitrate. The rest of the cycle is identical with the carbohydrate tricarboxylic cycle. Reference to this cycle illustrates several points of interest. It makes clear the pathway by which labelled carbon in acetate or acetoacetate may be transformed into D-glucose or glycogen. Since oxalacetate labelled in either carboxyl position is generated in the cycle, carboxyl-labelled... 

Steps 1, 3 phosphate transfers steps 2, 5, 8 i.somerizations step 4 retro-aldol reaction step 5 oxidation and nucleophilic acyl substitution steps 7, 10 phosphate transfers step 9 E2 dehydration Nucleophilic acyl substitution of acetyl dihydrolipoamide by coenzyme A Cl and C6 of glucose become -CH groups C3 and C4 become CO -Citrate and isocitrate E2 elimination of water, followed by conjugate addition (CH3)2CHCH2COCOr E2 reaction... 

Isocitrate lyase has been purified from the glyoxysomes of cucumber (Cucumis sativus) cotyledons. The glycoproteinaceous nature of the enzyme was demonstrated by periodate oxidation studies, and by the in vivo incorporation of 2-amino-2-deoxy-D-[ H]glucose into a species which was precipitable by antibodies to isocitrate lyase. 

PHB synthesis from glucose using Azotobacter beijerinkii revealed substantial amounts of polymer accumulation under oxygen limitation conditions. The key feature of control in A. beijerinckii is the pool size of acetyl-CoA, which may either be oxidized via the tricarboxylic acid (TCA) cycle or can serve as a substrate for PHB synthesis the diversion depends on environmental conditions, especially oxygen limitation, when the NADH/NAD ratio increases. Citrate synthase and isocitrate dehydrogenase are inhibited by NADH, and as a consequence, acetyl-CoA no longer enters the TCA cycle at the same rate. Instead acetyl-CoA is converted to acetoacetyl-CoA by p-ketothiolase, the first... 

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