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Kell blood group glycoprotein homolog or KEL, is an enzyme, part of the zinc endopeptidase of the neprilysin (NEP) group of proteins. KEL has a crucial part in the production of the potent bioactive ET-3, which also includes enzymes that are endothelin convertingenzymes (PEX, XCE, DINE &various NEP-like proteins). KEL uses a single disulfide bond to XK, a gated membranal transporter. The Kell antigen system that includes two proteins, is very crucial among blood group systems.

Glutamate Decarboxylase 2 (GAD2) is one of several forms of glutamic acid decarboxylase, identified as a main autoantigen in type II diabetes. The GAD2 enzyme is responsible for catalyzing the production of gamma-aminobutyric acid from L-glutamic acid. A pathogenic role for the GAD2 enzyme has been characterized in the human pancreas since it has been identified as an autoantibody and an autoreactive T cell target in type II diabetes. GAD2 gene may also have a role in the stiff man syndrome. In addition, GAD2 catalyzes the production of GABA.

Dehydrogenase/reductase SDR family member 4 (DHRS4) is a member of the short-chain dehydrogenases/reductases (SDR) family. DHRS4 reduces all trans retinal and 9-cis retinal. In addition, the DHRS4 protein can catalyze the oxidation of all trans retinol with NADP as cofactor, but with a much lower efficiency. Furthermore, DHRS4 reduces alkyl phenyl ketones and alpha dicarbonyl compounds with aromatic rings, such as pyrimidine 4 aldehyde, 3 benzoylpyridine, 4 benzoylpyridine, menadione and 4 hexanoylpyridine.

Lactate dehydrogenase (LDH) is an enzyme(EC1.1.1.27) present in a wide variety of organisms, including plants and animals.
A tetrameric enzyme that catalyses the interconversion of pyruvateand lactate with concomitant interconversion of NADH and NAD+. At high concentrations of pyruvate, the enzyme exhibits feedback inhibition and the rate of conversion of pyruvate to lactate is decreased. In vertebrates, genes for three different subunits (LDH-A, LDH-B and LDH-C) exist.

MTHFS is a cytosolic protein which takes part in the formate metabolic process. MTHFS along with a magnesium cofactor catalyzes the ATP-dependent reaction which reduces 5-formyltetrahydrofolate (5-MTHF) to 5,10-methenyltetrahydrofolate(MTHF). MTHF is the substrate used by MTHFR (methylenetetrahydrofolate reductase) to generate 5-MTHF. In addition, MTHF is a coenzyme used in thymidine biosynthesis by thymidylate synthase (FAD).

Threonyl-tRNA Synthetase is a member of the aminoacyl-tRNA synthetase family, key enzymes of protein biosynthesis which charge tRNA molecules with the respective amino acids. This 83 kDa protein is an autoantigen recognized by PL-7 antibodies which occur in a subset of patients with polymyositis and dermatomyositis. Preliminary data suggest that PL-7 antibodies (similar to Jo-1 antibodies) indicate an increased risk for lung involvement, but this needs to be confirmed for a larger number of cases.

6PGD is the 2nd dehydrogenase in the pentose phosphate shift. Pentose is crucial for the biosynthesis of nucleic acid. The pentose phosphate cycle is a prominent source of NADPH. 6PGD deficiency is mostly asymptomatic, and the inheritance of this deasis is autosomal dominant. PGD deficiency elevate the erythrocyte pyruvate kinase levels of activity & decreases glutathione synthetase, which causes hemolysis.

Rnase P protein, AKA rnpA, is an important enzyme consisting of the C5 protein (which encoded by rnpA) and the catalytic M1 RNA (encoded by rnpB) subunits. rnpA is ribonucleoprotein that catalyzes the removal of the 50- leader elements of precursor tRNAs and generates the mature 50-end of tRNAs. This step is critical for theformation of functional tRNA molecules in bacteria, archaea and eukarya. More importantly, it has lately been established that RNase P is essential for the endonucleolytic separation of certain polycistronic tRNA transcripts such as valV valW, leuQ leuP leuV and secG leuU. Therefore, it was hypothesized that the essential function of RNase P might be related to the complete absence of a particular tRNAthat was dependent on the enzyme for initial separation from polycistronic transcripts.

M2 autoantigen is a key mark of antimitochondrial autoantibodies (AMA), a typical serological feature in patients suffering from primary biliary cirrhosis (PBC) which is a serious autoimmune liver disease accompanied by damage to intrahepatic bile ducts. Molecular definition of the M2 antigen has displayed it as no less than 3 separate target proteins. The M2 role is like the so-called E2 subunits (or dihydrolipoamide transferases) of different mitochondrial dehydrogenase complexes:
*pyruvate dehydrogenase complex.
*branched chain 2-oxo-acid dehydrogenase complex.
*2-oxoglutarate dehydrogenase complex.
Biochemically, these complexes catalyze the oxidative decarboxylation of various alpha-keto-acid substrates and systematically engage with a prosthetic lipoamide group; they are situated in the mitochondrial matrix in association with the inner membrane. The most well-known reactivity of AMA positive PBC sera is against PDC-E2. Some patients have AMA which reacts with PDC-E2 alone (95%), but most patients also show reactivity against OGDC-E2 (39-88%) and/or BCOADC-E2 (53-55%). Actually, patients can be found with reactivity only against OGDC-E2 and/or BCOADC-E2 and no PDC-E2 autoantibodies. These patients will be overlooked in assays based on natural source-derived, predominantly PDC-E2-containing M2 antigen preparations.

E.Coli Acetate Kinase, also knowns as ACKA, catalyzes the formation of acetyl phosphate from acetate and ATP and also catalyzes the reverse reaction. ACKA takes part in synthesis of various ATP formed catabolically during anaerobic growth of the organism.

DDT is an enzyme that catayzes the tautomerization of D-dopachrome to give 5,6-dihydroxyindole (DHI). DDT is part of the family of lyases, specifically the carboxy-lyases, which cleave carbon-carbon bonds. DDT shares a homologous amino acid sequence (33% identical) with MIF and has similar tautomerase activity. DDT functions a proinflammatory cytokine.

NFNB demonstrates the capability to reduce quinines. NFNB enzyme activates prodrugs in antibody directed enzyme prodrug therapy. NFNB reduces nitrofurazone, quinones and anti-tumor agent CB1954 (5-(aziridin-1-yl)-2,4-dinitrobenzamide). The reduction of CB1954 results in the generation of cytotoxic species.

Carbonic anhydrase III is part of a multigene family that encodes carbonic anhydrase isozymes which are a class of metalloenzymes that catalyze the reversible hydration of carbon dioxide and are differentially expressed in various cell types. Carbonic anhydrase III expression is strictly tissue specific and present at high levels in skeletal muscle and much lower levels in cardiac and smooth muscle. CA3 catalyses swift conversion of carbon dioxide to bicarbonate and protons (CO2 + H2O = HCO3 + H+). CA3 participates in a variety of biological processes, including respiration, calcifica-tion, acid-base balance, bone resorption and the formation of aqueous humor, cerebrospinal fluid, saliva and gastric juice. CA3 includes a zinc ion in its active site and maintains acid-base balance in blood and other tissues, and to help transport carbon dioxide of tissues.

Catalase (CAT) is a key antioxidant enzyme in the body’s defense against oxidative stress. Furthermore, Catalase is a heme enzyme which is present in the peroxisome of virtually all aerobic cells. Catalase converts the reactive oxygen species hydrogen peroxide to water and oxygen and thus diminishes the toxic effects of hydrogen peroxide. Catalase stimulates growth of cells including T-cells, B-cells, myeloid leukemia cells, melanoma cells, mastocytoma cells and normal and transformed fibroblast cells. Catalase gene polymorphisms are linked with decreases in catalase activity nevertheless, to date, acatalasemia is the only disease known to be caused by the CAT gene.

Phosphomannomutase 2 (PMM2) is a member of the eukaryotic PMM family. Phosphomannomutase 2 is involved in the synthesis of the GDP-mannose and dolichol-phosphate-mannose required for a number of critical mannosyl transfer reactions. PMM2 catalyzes the isomerization of mannose 6-phosphate to mannose 1-phosphate. PMM2 mutations are linked to congenital disorders of glycosylation (CDG)-Ia, an autosomal recessive disorder characterized by central nervous system dysfunction and multiorgan failure.

LDHA catalyzes the conversion of L-lactate and NAD to pyruvate and NADH in the final step of anaerobic glycolysis. LDHA is localized primarily in muscle tissue and is part of the lactate dehydrogenase family. Mutations in LDHA have been linked to exertional myoglobinuria. LDH1 is decreased in essential thrombocythemia. LDHA is induced through a non-genomic pathway of estrogen action. Reduction in LDH-A activity results in stimulation of mitochondrial respiration and decrease of mitochondrial membrane potential.

Cathepsin-Z (CTSZ) is a lysosomal cysteine proteinase and member of the peptidase C1 family. CTSZ, which has been also known as cathepsin X and cathepsin P, exhibits carboxy-monopeptidase and carboxy-dipeptidase activities. CTSZ is expressed ubiquitously in cancer cell lines and primary tumors and, similar to other members of this family, takes part in tumorigenesis.

G3BP1 belongs to the heterogeneous nuclear RNA-binding proteins and is also an element of the Ras signal transduction pathway. G3BP1 is one of the DNA-unwinding enzymes that favors partially unwound 3'-tailed substrates and is also able to unwind partial RNA/DNA and RNA/RNA duplexes in an ATP-dependent fashion. G3BP1 binds specifically to the Ras-GTPase-activating protein by associating with its SH3 domain. In addition, G3BP1 cleaves exclusively between cytosine and adenine and cleaves MYC mRNA preferentially at the 3'-UTR.

Dual specificity phosphatase 13 (DUSP13) is a member of the protein-tyrosine phosphatase family. DUSP13 cooperates with protein kinases to control cell proliferation and differentiation. DUSP13 is engaged in the regulation of meiosis and/or differentiation of testicular germ cells in the course of spermatogenesis. DUSP13 demonstrates intrinsic phosphatase activity towards both phospho-seryl/threonyl and -tyrosyl residues of myelin basic protein, with similar specific activities in vitro.

Dual Specificity Phosphatase 26 (DUSP26) inhibits MAP kinase p38 by dephosphorylating it and inhibits p38-mediated apoptosis in anaplastic thyroid cancer cells. DUSP26 also induces activation of MAP kinase p38 and c-Jun N-terminal kinase. DUSP26 inactivates MAPK1 and MAPK3 which leads to dephosphorylation of heat shock factor protein 4 and a decrease in its DNA-binding activity.

Cathepsin-Z (CTSZ) is a lysosomal cysteine proteinase and a member of the peptidase C1 family. CTSZ, which is known also as cathepsin X and cathepsin P, exhibits carboxy-monopeptidase and carboxy-dipeptidase activities. CTSZ is expressed ubiquitously in cancer cell lines and primary tumors and as other members of this family, takes part in tumorigenesis.

Adenine DNA glycosylase (mutY) is an adenine DNA glycosylase active on DNA substrates including A/G, A/8-oxoG, or A/C mismatches and also has a weak guanine glycosylase activity on G/8- oxoG-containing DNA. mutY is essential for the prevention of mutations resulting from oxidative DNA impairment. Rising levels of mutY in A549 cells exposed to oxygen and infrared radiation leads to improvements in cell survival. mutY is common in neurons where mitochondrial genomes exposed to reactive oxygen species that damage DNA must uphold integrity over the whole mammalian life span.

Dual Specificity Phosphatase 22, also known as DUSP22, is a part of the protein-tyrosine phosphatase family which holds 1 tyrosine-protein phosphatase domain. DUSP22 activates the Jnk signaling pathway and dephosphorylates and deactivates p38 and stress-activated protein kinase/c-Jun N-terminal kinase (SAPK/JNK). DUSP22 interacts with MAPK1 and MAPK8.