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In chemistry, phosphorylation of a molecule is the attachment of a phosphoryl group. Together with its counterpart, dephosphorylation, it is critical for many cellular processes in biology. Protein phosphorylation is especially important for their function; for example, this modification activates almost half of the enzymes present in Saccharomyces cerevisiae, thereby regulating their function. Many proteins are phosphorylated temporarily, as are many sugars, lipids, and other biologically-relevant molecules.
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 takes place 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 glucose 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.
Pyruvate kinase is the enzyme involved in the last step of glycolysis. It catalyzes the transfer of a phosphate group from phosphoenolpyruvate (PEP) to adenosine diphosphate (ADP), yielding one molecule of pyruvate and one molecule of ATP. Pyruvate kinase was inappropriately named before it was recognized that it did not directly catalyze phosphorylation of pyruvate, which does not occur under physiological conditions. Pyruvate kinase is present in four distinct, tissue-specific isozymes in animals, each consisting of particular kinetic properties necessary to accommodate the variations in metabolic requirements of diverse tissues.
5' AMP-activated protein kinase or AMPK or 5' adenosine monophosphate-activated protein kinase is an enzyme that plays a role in cellular energy homeostasis, largely to activate glucose and fatty acid uptake and oxidation when cellular energy is low. It belongs to a highly conserved eukaryotic protein family and its orthologues are SNF1 in yeast, and SnRK1 in plants. It consists of three proteins (subunits) that together make a functional enzyme, conserved from yeast to humans. It is expressed in a number of tissues, including the liver, brain, and skeletal muscle. In response to binding AMP and ADP, the net effect of AMPK activation is stimulation of hepatic fatty acid oxidation, ketogenesis, stimulation of skeletal muscle fatty acid oxidation and glucose uptake, inhibition of cholesterol synthesis, lipogenesis, and triglyceride synthesis, inhibition of adipocyte lipogenesis, inhibition of adipocyte lipolysis, and modulation of insulin secretion by pancreatic beta-cells.
Glucokinase is an enzyme that facilitates phosphorylation of glucose to glucose-6-phosphate. Glucokinase occurs in cells in the liver and pancreas of humans and most other vertebrates. In each of these organs it plays an important role in the regulation of carbohydrate metabolism by acting as a glucose sensor, triggering shifts in metabolism or cell function in response to rising or falling levels of glucose, such as occur after a meal or when fasting. Mutations of the gene for this enzyme can cause unusual forms of diabetes or hypoglycemia.
The insulin receptor (IR) is a transmembrane receptor that is activated by insulin, IGF-I, IGF-II and belongs to the large class of tyrosine kinase receptors. Metabolically, the insulin receptor plays a key role in the regulation of glucose homeostasis, a functional process that under degenerate conditions may result in a range of clinical manifestations including diabetes and cancer. Insulin signalling controls access to blood glucose in body cells. When insulin falls, especially in those with high insulin sensitivity, body cells begin only to have access to lipids that do not require transport across the membrane. So, in this way, insulin is the key regulator of fat metabolism as well. Biochemically, the insulin receptor is encoded by a single gene INSR, from which alternate splicing during transcription results in either IR-A or IR-B isoforms. Downstream post-translational events of either isoform result in the formation of a proteolytically cleaved α and β subunit, which upon combination are ultimately capable of homo or hetero-dimerisation to produce the ≈320 kDa disulfide-linked transmembrane insulin receptor.
A mitogen-activated protein kinase is a type of protein kinase that is specific to the amino acids serine and threonine. MAPKs are involved in directing cellular responses to a diverse array of stimuli, such as mitogens, osmotic stress, heat shock and proinflammatory cytokines. They regulate cell functions including proliferation, gene expression, differentiation, mitosis, cell survival, and apoptosis.
Glycated hemoglobin is a form of hemoglobin (Hb) that is chemically linked to a sugar. Most monosaccharides, including glucose, galactose and fructose, spontaneously bond with hemoglobin, when present in the bloodstream of humans. However, glucose is less likely to do so than galactose and fructose, which may explain why glucose is used as the primary metabolic fuel in humans.
The glucokinase regulatory protein (GKRP) also known as glucokinase regulator (GCKR) is a protein produced in hepatocytes. GKRP binds and moves glucokinase (GK), thereby controlling both activity and intracellular location of this key enzyme of glucose metabolism.
Phosphofructokinase-2 (6-phosphofructo-2-kinase, PFK-2) or fructose bisphosphatase-2 (FBPase-2), is an enzyme indirectly responsible for regulating the rates of glycolysis and gluconeogenesis in cells. It catalyzes formation and degradation of a significant allosteric regulator, fructose-2,6-bisphosphate (Fru-2,6-P2) from substrate fructose-6-phosphate. Fru-2,6-P2 contributes to the rate-determining step of glycolysis as it activates enzyme phosphofructokinase 1 in the glycolysis pathway, and inhibits fructose-1,6-bisphosphatase 1 in gluconeogenesis. Since Fru-2,6-P2 differentially regulates glycolysis and gluconeogenesis, it can act as a key signal to switch between the opposing pathways. Because PFK-2 produces Fru-2,6-P2 in response to hormonal signaling, metabolism can be more sensitively and efficiently controlled to align with the organism's glycolytic needs.This enzyme participates in fructose and mannose metabolism. The enzyme is important in the regulation of hepatic carbohydrate metabolism and is found in greatest quantities in the liver, kidney and heart. In mammals, several genes often encode different isoforms, each of which differs in its tissue distribution and enzymatic activity. The family described here bears a resemblance to the ATP-driven phospho-fructokinases, however, they share little sequence similarity, although a few residues seem key to their interaction with fructose 6-phosphate.
Fructosamines are compounds that result from glycation reactions between a sugar and a primary amine, followed by isomerization via the Amadori rearrangement. Biologically, fructosamines are recognized by fructosamine-3-kinase, which may trigger the degradation of advanced glycation end-products. Fructosamine can also refer to the specific compound 1-amino-1-deoxy-D-fructose (isoglucosamine), first synthesized by Nobel laureate Hermann Emil Fischer in 1886.
Protein kinase C delta type is an enzyme that in humans is encoded by the PRKCD gene.
Eukaryotic translation initiation factor 2-alpha kinase 3, also known as protein kinase R (PKR)-like endoplasmic reticulum kinase (PERK), is an enzyme that in humans is encoded by the EIF2AK3 gene.
Glucosamine—fructose-6-phosphate aminotransferase isomerizing 1 is an enzyme that in humans is encoded by the GFPT1 gene.
Fructosamine-3-kinase is an enzyme that in humans is encoded by the FN3K gene.
Ketosamine-3-kinase is an enzyme that in humans is encoded by the FN3KRP (fructosamine-3-kinase-related-protein) gene.
3-Deoxyglucosone (3DG) is a sugar that is notable because it is a marker for diabetes. 3DG reacts with protein to form advanced glycation end-products (AGEs), which contribute to diseases such as the vascular complications of diabetes, atherosclerosis, hypertension, Alzheimer's disease, inflammation, and aging.
Protein-fructosamine 3-kinase (EC 2.7.1.171, FN3K, fructosamine 3-kinase) is an enzyme with systematic name ATP:(protein)-N6-D-fructosyl-L-lysine 3-phosphotransferase. This enzyme catalyses the following chemical reaction
Protein-ribulosamine 3-kinase (EC 2.7.1.172, FN3KRP, FN3K-related protein, FN3K-RP, ketosamine 3-kinase 2, fructosamine-3-kinase-related protein, ribulosamine/erythrulosamine 3-kinase, ribulosamine 3-kinase) is an enzyme with systematic name ATP:(protein)-N6-D-ribulosyl-L-lysine 3-phosphotransferase. This enzyme catalyses the following chemical reaction
Fructoselysine is an Amadori adduct of glucose to lysine.
References
- ↑ Delpierre G, Rider MH, Collard F, Stroobant V, Vanstapel F, Santos H, Van Schaftingen E (October 2000). "Identification, cloning, and heterologous expression of a mammalian fructosamine-3-kinase". Diabetes. 49 (10): 1627–34. doi:10.2337/diabetes.49.10.1627. PMID 11016445.
- ↑ Armbruster DA (December 1987). "Fructosamine: structure, analysis, and clinical usefulness". Clin. Chem. 33 (12): 2153–63. doi:10.1093/clinchem/33.12.2153. PMID 3319287.
- ↑ Collard F, Delpierre G, Stroobant V, Matthijs G, Van Schaftingen E (December 2003). "A mammalian protein homologous to fructosamine-3-kinase is a ketosamine-3-kinase acting on psicosamines and ribulosamines but not on fructosamines". Diabetes. 52 (12): 2888–95. doi: 10.2337/diabetes.52.12.2888 . PMID 14633848.
- ↑ Delvalle JA, Asensio C (August 1978). "Distribution of adenosine 5'-triphosphate (ATP)-dependent hexose kinases in microorganisms". BioSystems. 10 (3): 265–82. doi:10.1016/0303-2647(78)90008-4. PMID 214181.