The citric acid cycle —also known as the Krebs cycle, Szent-Györgyi-Krebs cycle or the TCA cycle (tricarboxylic acid cycle)—is a series of chemical reactions to release stored energy through the oxidation of acetyl-CoA derived from carbohydrates, fats, and proteins. The Krebs cycle is used by organisms that respire (as opposed to organisms that ferment) to generate energy, either by anaerobic respiration or aerobic respiration. In addition, the cycle provides precursors of certain amino acids, as well as the reducing agent NADH, that are used in numerous other reactions. Its central importance to many biochemical pathways suggests that it was one of the earliest components of metabolism. Even though it is branded as a 'cycle', it is not necessary for metabolites to follow only one specific route; at least three alternative segments of the citric acid cycle have been recognized.
Pyruvic acid (IUPAC name: 2-oxopropanoic acid, also called acetoic acid) (CH3COCOOH) is the simplest of the alpha-keto acids, with a carboxylic acid and a ketone functional group. Pyruvate, the conjugate base, CH3COCOO−, is an intermediate in several metabolic pathways throughout the cell.
Glucose-6-phosphate dehydrogenase deficiency (G6PDD), which is the most common enzyme deficiency worldwide, is an inborn error of metabolism that predisposes to red blood cell breakdown. Most of the time, those who are affected have no symptoms. Following a specific trigger, symptoms such as yellowish skin, dark urine, shortness of breath, and feeling tired may develop. Complications can include anemia and newborn jaundice. Some people never have symptoms.
Glucose 6-phosphate is a glucose sugar phosphorylated at the hydroxy group on carbon 6. This dianion is very common in cells as the majority of glucose entering a cell will become phosphorylated in this way.
Pyrroloquinoline quinone (PQQ), also called methoxatin, is a redox cofactor and antioxidant.
Nicotinamide adenine dinucleotide phosphate, abbreviated NADP+ or, in older notation, TPN (triphosphopyridine nucleotide), is a cofactor used in anabolic reactions, such as the Calvin cycle and lipid and nucleic acid syntheses, which require NADPH as a reducing agent ('hydrogen source'). NADPH is the reduced form of NADP+, the oxidized form. NADP+ is used by all forms of cellular life.
The pentose phosphate pathway is a metabolic pathway parallel to glycolysis. It generates NADPH and pentoses as well as ribose 5-phosphate, a precursor for the synthesis of nucleotides. While the pentose phosphate pathway does involve oxidation of glucose, its primary role is anabolic rather than catabolic. The pathway is especially important in red blood cells (erythrocytes). The reactions of the pathway were elucidated in the early 1950s by Bernard Horecker and co-workers.
Glucose-6-phosphate dehydrogenase (G6PD or G6PDH) (EC 1.1.1.49) is a cytosolic enzyme that catalyzes the chemical reaction
The malate–aspartate shuttle is a biochemical system for translocating electrons produced during glycolysis across the semipermeable inner membrane of the mitochondrion for oxidative phosphorylation in eukaryotes. These electrons enter the electron transport chain of the mitochondria via reduction equivalents to generate ATP. The shuttle system is required because the mitochondrial inner membrane is impermeable to NADH, the primary reducing equivalent of the electron transport chain. To circumvent this, malate carries the reducing equivalents across the membrane.
In enzymology, aldose reductase is a cytosolic NADPH-dependent oxidoreductase that catalyzes the reduction of a variety of aldehydes and carbonyls, including monosaccharides. It is primarily known for catalyzing the reduction of glucose to sorbitol, the first step in polyol pathway of glucose metabolism.
Pyruvate dehydrogenase kinase is a kinase enzyme which acts to inactivate the enzyme pyruvate dehydrogenase by phosphorylating it using ATP.
Sorbitol dehydrogenase is a cytosolic enzyme. In humans this protein is encoded by the SORD gene.
UDP-glucuronic acid is a sugar used in the creation of polysaccharides and is an intermediate in the biosynthesis of ascorbic acid. It also participates in the heme degradation process of human.
In enzymology, a glucose 1-dehydrogenase (NADP+) (EC 1.1.1.119) is an enzyme that catalyzes the chemical reaction
UDP-glucose 6-dehydrogenase is a cytosolic enzyme that in humans is encoded by the UGDH gene.
In enzymology, a quinoprotein glucose dehydrogenase is an enzyme that catalyzes the chemical reaction
Pyruvate dehydrogenase lipoamide kinase isozyme 4, mitochondrial (PDK4) is an enzyme that in humans is encoded by the PDK4 gene. It codes for an isozyme of pyruvate dehydrogenase kinase.
GDH/6PGL endoplasmic bifunctional protein is a protein that in humans is encoded by the H6PD gene.
6-Phosphogluconate dehydrogenase deficiency, or partial deficiency, is an autosomal hereditary disease characterized by abnormally low levels of 6-phosphogluconate dehydrogenase (6PGD), a metabolic enzyme involved in the Pentose phosphate pathway. It is very important in the metabolism of red blood cells (erythrocytes). 6PDG deficiency affects less than 1% of the population, and studies suggest that there may be race variant involved in many of the reported cases. Although it is similar, 6PDG deficiency is not linked to glucose-6-phosphate dehydrogenase (G6PD) deficiency, as they are located on different chromosomes. However, a few people have had both of these metabolic diseases.
Pyruvate decarboxylation or pyruvate oxidation, also known as the link reaction, Swanson Conversion, or oxidative decarboxylation of pyruvate, is the conversion of pyruvate into acetyl-CoA by the enzyme complex pyruvate dehydrogenase complex.
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