Term
| pyruvate dehydrogenase (PDH) complex |
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Definition
| oxidizes pyruvate (derived from glucose & other sugars by glycolysis) to acetyl-CoA & CO2; a cluster of enzymes (multiple copies of 3 enzymes) located in the mitochondria of eukaryotic cells & in the cytosol of bacteria |
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Term
| oxidative decarboxylation |
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Definition
| ex) the overall reaction catalyzed by the pyruvate dehydrogenase complex; an irreversible oxidation process in which the carboxyl group is removed from pyruvate as a molecule of CO2 & the two remaining carbons become the acetyl group of acetyl-CoA |
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Term
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Definition
| when acyl groups are covalently linked to the thiol group |
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Term
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Definition
| the fifth cofactor of the PDH complex; has two thiol groups that can undergo reversible oxidation to a disulfide bond similar to that between two Cys residues in a protein |
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Term
| 3 enzymes in the PDH complex (each is present in multiple copies) |
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Definition
1. pyruvate dehydrogenase
2. dihydrolipoyl transacetylase
3. dihydrolipoyl dehydrogenase |
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Term
| 8 steps to the citric acid cycle |
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Definition
1. formation of citrate
2. formation of isocitrate via cis-aconitate
3. oxidation of isocitrate to alpha-ketoglutarate & CO2
4. oxidation of alpha-ketoglutarate to succinyl-CoA & CO2
5. conversion of succinyl-CoA to succinate
6. oxidation of succinate to fumarate
7. hydration of fumarate to malate
8. oxidation of malate to oxaloacetate |
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Term
| What is the first reaction of the citric acid cycle (formation of citrate)? |
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Definition
| the condensation of acetyl-CoA with oxaloacetate to form citrate (catalyzed by citrate synthase) |
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Term
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Definition
| the enzyme that 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 |
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Term
| What does the iron-sulfur center of aconitase do for the formation of isocitrate via cis-aconitate? |
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Definition
| it acts both in the binding of the substrate at the active site & in the catalytic addition or removal of H2O |
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Term
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Definition
| catalyzes oxidative decarboxylation of isocitrate to form alpha-ketoglutarate |
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Term
| How does the oxidation of alpha-ketoglutarate to succinyl-CoA & CO2 occur? |
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Definition
| an oxidative decarboxylation in which alpha-ketoglutarate is converted to succinyl-CoA & CO2 by the action of the alpha-ketoglutarate dehydrogenase complex; NAD+ serves as the electron acceptor & CoA as the carrier of the succinyl group |
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Term
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Definition
| when the genes for an enzyme with one substrate specificity give rise (during evolution) to closely related enzymes with different substrate specificities but the same enzymatic mechanism |
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Term
| What is indicated in the name of "succinyl-CoA synthetase" (AKA "succinic thiokinase") about the reaction it catalyzes? |
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Definition
| the participation of a nucleoside triphosphate in the reaction |
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Term
| nucleoside diphosphate kinase |
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Definition
| catalyzes the reversible donation of the terminal phosphoryl group of the GTP (formed by succinyl-CoA synthetase) to ADP to form ATP |
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Term
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Definition
| the flavo-protein that oxidizes the succinate (formed from succinyl-CoA) to fumarate |
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Term
| fumarase (fumarate hydratase) |
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Definition
| catalyzes the reversible hydration of fumarate to L-malate |
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Term
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Definition
| an NAD-linked molecule that catalyzes the oxidation of L-malate to oxaloacetate in the last reaction of the citric acid cycle |
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Term
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Definition
| ex) the citric acid cycle in aerobic organisms; a pathway that serves in both catabolic & anabolic processes |
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Term
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Definition
| reactions that replenish intermediates of the citric acid cycle as they are removed to serve as biosynthetic precursors |
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Term
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Definition
| catalyzes the most important anaplerotic reaction in mammalian liver & kidney: the reversible carboxylation of pyruvate by CO2 to form oxaloacetate |
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Term
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Definition
| the vitamin required for the pyruvate carboxylase reaction; the prosthetic group of the enzyme |
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Term
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Definition
| the protein found in egg whites in a large amount; binds very tightly to biotin & prevents its absorption into the intestine |
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