Lysine is an α-amino acid that is a precursor to many proteins. Lysine contains an α-amino group, an α-carboxylic acid group, and a side chain (CH2)4NH2, and so it is classified as a basic, charged, aliphatic amino acid. It is encoded by the codons AAA and AAG. Like almost all other amino acids, the α-carbon is chiral and lysine may refer to either enantiomer or a racemic mixture of both. For the purpose of this article, lysine will refer to the biologically active enantiomer L-lysine, where the α-carbon is in the S configuration.
Succinic acid is a dicarboxylic acid with the chemical formula (CH2)2(CO2H)2. In living organisms, succinic acid takes the form of an anion, succinate, which has multiple biological roles as a metabolic intermediate being converted into fumarate by the enzyme succinate dehydrogenase in complex 2 of the electron transport chain which is involved in making ATP, and as a signaling molecule reflecting the cellular metabolic state.
Inborn errors of metabolism form a large class of genetic diseases involving congenital disorders of enzyme activities. The majority are due to defects of single genes that code for enzymes that facilitate conversion of various substances (substrates) into others (products). In most of the disorders, problems arise due to accumulation of substances which are toxic or interfere with normal function, or due to the effects of reduced ability to synthesize essential compounds. Inborn errors of metabolism are often referred to as congenital metabolic diseases or inherited metabolic disorders. Another term used to describe these disorders is "enzymopathies". This term was created following the study of biodynamic enzymology, a science based on the study of the enzymes and their products. Finally, inborn errors of metabolism were studied for the first time by British physician Archibald Garrod (1857–1936), in 1908. He is known for work that prefigured the "one gene–one enzyme" hypothesis, based on his studies on the nature and inheritance of alkaptonuria. His seminal text, Inborn Errors of Metabolism, was published in 1923.
The oxoglutarate dehydrogenase complex (OGDC) or α-ketoglutarate dehydrogenase complex is an enzyme complex, most commonly known for its role in the citric acid cycle.
Glutaric acidemia type 1 (GA1) is an inherited disorder in which the body is unable to completely break down the amino acids lysine, hydroxylysine and tryptophan. Excessive levels of their intermediate breakdown products can accumulate and cause damage to the brain, but particularly the basal ganglia, which are regions that help regulate movement. GA1 causes secondary carnitine deficiency, as glutaric acid, like other organic acids, is detoxified by carnitine. Mental retardation may occur.
3 Hydroxyisobutyric aciduria is a rare metabolic disorder in which the body is unable to metabolize certain amino acids. This causes a toxic buildup of specific acids called organic acids in the blood, tissues, and urine. The precise underlying cause remains unknown. Some cases may be caused by mutations in the ALDH6A1 gene and inherited autosomally recessively.
Succinic semialdehyde dehydrogenase deficiency (SSADHD) is a rare autosomal recessive disorder of the degradation pathway of the inhibitory neurotransmitter γ-aminobutyric acid, or GABA. The disorder has been identified in approximately 350 families, with a significant proportion being consanguineous families. The first case was identified in 1981 and published in a Dutch clinical chemistry journal that highlighted a number of neurological conditions such as delayed intellectual, motor, speech, and language as the most common manifestations. Later cases reported in the early 1990s began to show that hypotonia, hyporeflexia, seizures, and a nonprogressive ataxia were frequent clinical features as well.
Malonyl-CoA decarboxylase, is found in bacteria and humans and has important roles in regulating fatty acid metabolism and food intake, and it is an attractive target for drug discovery. It is an enzyme associated with Malonyl-CoA decarboxylase deficiency. In humans, it is encoded by the MLYCD gene.
Glutaryl-CoA dehydrogenase (GCDH) is an enzyme encoded by the GCDH gene on chromosome 19. The protein belongs to the acyl-CoA dehydrogenase family (ACD). It catalyzes the oxidative decarboxylation of glutaryl-CoA to crotonyl-CoA and carbon dioxide in the degradative pathway of L-lysine, L-hydroxylysine, and L-tryptophan metabolism. It uses electron transfer flavoprotein as its electron acceptor. The enzyme exists in the mitochondrial matrix as a homotetramer of 45-kD subunits. Mutations in this gene result in the metabolic disorder glutaric aciduria type 1, which is also known as glutaric acidemia type I. Alternative splicing of this gene results in multiple transcript variants.
3-Methylglutaconyl-CoA hydratase, also known as MG-CoA hydratase and AUH, is an enzyme encoded by the AUH gene on chromosome 19. It is a member of the enoyl-CoA hydratase/isomerase superfamily, but it is the only member of that family that is able to bind to RNA. Not only does it bind to RNA, AUH has also been observed to be involved in the metabolic enzymatic activity, making it a dual-role protein. Mutations of this gene have been found to cause a disease called 3-Methylglutaconic Acuduria Type 1.
Electron-transferring-flavoprotein dehydrogenase is an enzyme that transfers electrons from electron-transferring flavoprotein in the mitochondrial matrix, to the ubiquinone pool in the inner mitochondrial membrane. It is part of the electron transport chain. The enzyme is found in both prokaryotes and eukaryotes and contains a flavin and FE-S cluster. In humans, it is encoded by the ETFDH gene. Deficiency in ETF dehydrogenase causes the human genetic disease multiple acyl-CoA dehydrogenase deficiency.
L-2-hydroxyglutarate dehydrogenase, mitochondrial is an enzyme that in humans is encoded by the L2HGDH gene, also known as C14orf160, on chromosome 14.
Alpha-aminoadipic semialdehyde synthase is an enzyme encoded by the AASS gene in humans and is involved in their major lysine degradation pathway. It is similar to the separate enzymes coded for by the LYS1 and LYS9 genes in yeast, and related to, although not similar in structure, the bifunctional enzyme found in plants. In humans, mutations in the AASS gene, and the corresponding alpha-aminoadipic semialdehyde synthase enzyme are associated with familial hyperlysinemia. This rare disease is inherited in an autosomal recessive pattern and patients often have no clinical symptoms.
Methylmalonate-semialdehyde dehydrogenase [acylating], mitochondrial (MMSDH) is an enzyme that in humans is encoded by the ALDH6A1 gene.
The α-aminoadipate pathway is a biochemical pathway for the synthesis of the amino acid L-lysine. In the eukaryotes, this pathway is unique to several species of yeast, higher fungi, and the euglenids. It has also been reported from bacteria of the genus Thermus and also in Pyrococcus horikoshii, potentially suggesting a wider distribution than previously thought. This uniqueness of the pathway makes it a potentially interesting target for antimycotics.
Dehydrogenase E1 and transketolase domain containing 1 is a protein that in humans is encoded by the DHTKD1 gene. This gene encodes a component of a mitochondrial 2-oxoglutarate-dehydrogenase-complex-like protein involved in the degradation pathways of several amino acids, including lysine. Mutations in this gene are associated with 2-aminoadipic 2-oxoadipic aciduria and Charcot-Marie-Tooth Disease Type 2Q.
Metabolite damage can occur through enzyme promiscuity or spontaneous chemical reactions. Many metabolites are chemically reactive and unstable and can react with other cell components or undergo unwanted modifications. Enzymatically or chemically damaged metabolites are always useless and often toxic. To prevent toxicity that can occur from the accumulation of damaged metabolites, organisms have damage-control systems that:
- Reconvert damaged metabolites to their original, undamaged form
- Convert a potentially harmful metabolite to a benign one
- Prevent damage from happening by limiting the build-up of reactive, but non-damaged metabolites that can lead to harmful products
α-Aminoadipic acid is one of the metabolic precursor in the biosynthesis of lysine through α-aminoadipate pathway. Its conjugate base is α-aminoadipate, which is the prevalent form at physiological pH.
The citrate-malate shuttle is a series of chemical reactions, commonly referred to as a biochemical cycle or system, that transports acetyl-CoA in the mitochondrial matrix across the inner and outer mitochondrial membranes for fatty acid synthesis. Mitochondria are enclosed in a double membrane. As the inner mitochondrial membrane is impermeable to acetyl-CoA, the shuttle system is essential to fatty acid synthesis in the cytosol. It plays an important role in the generation of lipids in the liver.
Combined malonic and methylmalonic aciduria (CMAMMA), also called combined malonic and methylmalonic acidemia is an inherited metabolic disease characterized by elevated levels of malonic acid and methylmalonic acid. However, the methylmalonic acid levels exceed those of malonic acid. CMAMMA is not only an organic aciduria but also a defect of mitochondrial fatty acid synthesis (mtFASII). Some researchers have hypothesized that CMAMMA might be one of the most common forms of methylmalonic acidemia, and possibly one of the most common inborn errors of metabolism. Due to being infrequently diagnosed, it most often goes undetected.
