Gluconeogenesis (GNG) is a metabolic pathway that results in the generation of glucose from certain non-carbohydrate carbon substrates. It is a ubiquitous process, present in plants, animals, fungi, bacteria, and other microorganisms. In vertebrates, gluconeogenesis occurs mainly in the liver and, to a lesser extent, in the cortex of the kidneys. It is one of two primary mechanisms – the other being degradation of glycogen (glycogenolysis) – used by humans and many other animals to maintain blood sugar levels, avoiding low levels (hypoglycemia). In ruminants, because dietary carbohydrates tend to be metabolized by rumen organisms, gluconeogenesis occurs regardless of fasting, low-carbohydrate diets, exercise, etc. In many other animals, the process occurs during periods of fasting, starvation, low-carbohydrate diets, or intense exercise.
Oxaloacetic acid (also known as oxalacetic acid or OAA) is a crystalline organic compound with the chemical formula HO2CC(O)CH2CO2H. Oxaloacetic acid, in the form of its conjugate base oxaloacetate, is a metabolic intermediate in many processes that occur in animals. It takes part in gluconeogenesis, the urea cycle, the glyoxylate cycle, amino acid synthesis, fatty acid synthesis and the citric acid cycle.
Mixed inhibition is a type of enzyme inhibition in which the inhibitor may bind to the enzyme whether or not the enzyme has already bound the substrate but has a greater affinity for one state or the other. It is called "mixed" because it can be seen as a conceptual "mixture" of competitive inhibition, in which the inhibitor can only bind the enzyme if the substrate has not already bound, and uncompetitive inhibition, in which the inhibitor can only bind the enzyme if the substrate has already bound. If the ability of the inhibitor to bind the enzyme is exactly the same whether or not the enzyme has already bound the substrate, it is known as a non-competitive inhibitor. Non-competitive inhibition is sometimes thought of as a special case of mixed inhibition.
Malate dehydrogenase (EC 1.1.1.37) (MDH) is an enzyme that reversibly catalyzes the oxidation of malate to oxaloacetate using the reduction of NAD+ to NADH. This reaction is part of many metabolic pathways, including the citric acid cycle. Other malate dehydrogenases, which have other EC numbers and catalyze other reactions oxidizing malate, have qualified names like malate dehydrogenase (NADP+).
Pyruvate carboxylase (PC) encoded by the gene PC is an enzyme of the ligase class that catalyzes the physiologically irreversible carboxylation of pyruvate to form oxaloacetate (OAA).
Phosphoenolpyruvate is the ester derived from the enol of pyruvate and phosphate. It exists as an anion. PEP is an important intermediate in biochemistry. It has the highest-energy phosphate bond found in organisms, and is involved in glycolysis and gluconeogenesis. In plants, it is also involved in the biosynthesis of various aromatic compounds, and in carbon fixation; in bacteria, it is also used as the source of energy for the phosphotransferase system.
Phosphopyruvate hydratase, usually known as enolase, is a metalloenzyme (EC 4.2.1.11) that catalyses the conversion of 2-phosphoglycerate (2-PG) to phosphoenolpyruvate (PEP), the ninth and penultimate step of glycolysis. The chemical reaction is:
In biochemistry, mixed acid fermentation is the metabolic process by which a six-carbon sugar is converted into a complex and variable mixture of acids. It is an anaerobic (non-oxygen-requiring) fermentation reaction that is common in bacteria. It is characteristic for members of the Enterobacteriaceae, a large family of Gram-negative bacteria that includes E. coli.
Carboxy-lyases, also known as decarboxylases, are carbon–carbon lyases that add or remove a carboxyl group from organic compounds. These enzymes catalyze the decarboxylation of amino acids, beta-keto acids and alpha-keto acids.
Phosphoenolpyruvate carboxylase (also known as PEP carboxylase, PEPCase, or PEPC; EC 4.1.1.31, PDB ID: 3ZGE) is an enzyme in the family of carboxy-lyases found in plants and some bacteria that catalyzes the addition of bicarbonate (HCO3−) to phosphoenolpyruvate (PEP) to form the four-carbon compound oxaloacetate and inorganic phosphate:
Phosphoenolpyruvate carboxykinase is an enzyme in the lyase family used in the metabolic pathway of gluconeogenesis. It converts oxaloacetate into phosphoenolpyruvate and carbon dioxide.
Phosphoenolpyruvate carboxykinase (diphosphate) (EC 4.1.1.38) is an enzyme with systematic name diphosphate:oxaloacetate carboxy-lyase (transphosphorylating; phosphoenolpyruvate-forming). This enzyme catalyses the following chemical reaction
Oxaloacetate decarboxylase is a carboxy-lyase involved in the conversion of oxaloacetate into pyruvate.
Propionyl-CoA carboxylase (EC 6.4.1.3, PCC) catalyses the carboxylation reaction of propionyl-CoA in the mitochondrial matrix. PCC has been classified both as a ligase and a lyase. The enzyme is biotin-dependent. The product of the reaction is (S)-methylmalonyl CoA.
Malate dehydrogenase (oxaloacetate-decarboxylating) (NADP+) (EC 1.1.1.40) or NADP-malic enzyme (NADP-ME) is an enzyme that catalyzes the chemical reaction in the presence of a bivalent metal ion:
In enzymology, a pyruvate, water dikinase (EC 2.7.9.2) is an enzyme that catalyzes the chemical reaction
Phosphoenolpyruvate carboxykinase 1 (soluble), also known as PCK1, is an enzyme which in humans is encoded by the PCK1 gene.
Pyruvate cycling commonly refers to an intracellular loop of spatial movements and chemical transformations involving pyruvate. Spatial movements occur between mitochondria and cytosol and chemical transformations create various Krebs cycle intermediates. In all variants, pyruvate is imported into the mitochondrion for processing through part of the Krebs cycle. In addition to pyruvate, alpha-ketoglutarate may also be imported. At various points, the intermediate product is exported to the cytosol for additional transformations and then re-imported. Three specific pyruvate cycles are generally considered, each named for the principal molecule exported from the mitochondrion: malate, citrate, and isocitrate. Other variants may exist, such as dissipative or "futile" pyruvate cycles.
Phosphoenolpyruvate carboxykinase 2, mitochondrial, is an isozyme of phosphoenolpyruvate carboxykinase that in humans is encoded by the PCK2 gene on chromosome 14. This gene encodes a mitochondrial enzyme that catalyzes the conversion of oxaloacetate (OAA) to phosphoenolpyruvate (PEP) in the presence of guanosine triphosphate (GTP). A cytosolic form of this protein is encoded by a different gene and is the key enzyme of gluconeogenesis in the liver. Alternatively spliced transcript variants have been described.[provided by RefSeq, Apr 2014]
Merton Franklin Utter was an American microbiologist and biochemist.
