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Thymidylate synthase catalyzes the methylation of deoxyuridylate to deoxythymidylate using 5,10-methylenetetrahydrofolate as a cofactor which maintains the dTMP (thymidine-5-prime monophosphate) pool vital for DNA replication and repair. Thymidylate synthase plays an important role as a cancer chemotherapeutic agent. Thymidylate synthase is the primary site of action for 5-fluorouracil, 5-fluoro-2-prime-deoxyuridine, and several folate analogs.

Creatine Kinase, Mitochondrial 2 (CKMT2) is a member of the ATP:guanido phosphotransferase family. CKMT2 is responsible for the transfer of high energy phosphate from mitochondria to the cytosolic carrier, creatine. CKMT2 reversibly catalyzes the transfer of phosphate between ATP and various phosphogens (e.g. creatine phosphate). Creatine kinase isoenzymes have a principal role in energy transduction in tissues with large, variable energy demands, such as skeletal muscle, heart, brain and spermatozoa. Mitochondrial creatine kinase occurs in 2 different oligomeric forms: dimers and octamers, contrary to the exclusively dimeric cytosolic creatine kinase isoenzymes. The CKMT2 gene contains sequences homologous to a number of motifs which are shared among some nuclear genes encoding mitochondrial proteins and therefore may be crucial for the coordinated activation of these genes during mitochondrial biogenesis.

Mitochondrial Ribosomal Protein L1 (MRPL1) exists as a component of the 39S ribosomal subunit and operates in conjunction with other MRPs to mediate protein synthesis. Mitochondrial ribosomes consist of a large 39S subunit and a small 28S subunit, both of which are consist of multiple mitochondrial ribosomal proteins (MRPs) that are encoded by nuclear genes and are vital for protein synthesis within mitochondria. MRPL1 exists as 2 isoforms produced by alternative splicing. Isoform 1 of MRPL1 is ubiquitously expressed while isoform 2 is particularly expressed in heart.

Mitochondrial Ribosomal Protein L48, also known as MRPL48, is a mammalian mitochondrial ribosomal protein which assists in protein synthesis within the mitochondrion. Mitochondrial ribosomes, mitoribosomes, consist of a small 28S subunit and a large 39S subunit. They include an estimated 75% protein to rRNA composition while comparing to prokaryotic ribosomes, where this ratio is reversed.An additional dissimilarity between mammalian mitoribosomes & prokaryotic ribosomes is that the latter contain a 5S rRNA. Between different species, the proteins containing the mitoribosome differ very much in sequence, as well as in biochemical properties from time to time, which prevents easy recognition through sequence homology. MRPL48 encodes a 39S subunit protein. A pseudogene corresponding to MRPL48 is found on chromosome 6p.

CKMT1A is in charge of the transfer of high energy phosphate from mitochondria to the cytosolic carrier, creatine. CKMT1A is a member of the creatine kinase isoenzyme family and exists as two isoenzymes, sarcomeric MtCK and ubiquitous MtCK, encoded by separate genes. Mitochondrial creatine kinase arises in two different oligomeric forms: dimers and octamers, unlike the exclusively dimeric cytosolic creatine kinase isoenzymes. Numerous malignant cancers with poor prognosis have displayed overexpression of ubiquitous mitochondrial creatine kinase which is linked to high energy turnover and inability to remove cancer cells through apoptosis.

Apoptosis-Inducing Factor, Mitochondrion-Associated, 1 (AIFM1) is a mitochondrial protein which translocates to the nucleus once apoptosis has been initiated. AIFM1 causes DNA fragmentation and chromatin condensation and also triggers the release of cytochrome c and caspase-9 from mitochondria. Bcl-2 overexpression prevents the release of AIFM1 from mitochondria, but doesn’t block its apoptogenic activity.

NADH Dehydrogenase1 Alpha Subcomplex 4 (NDUFA4) is a member of the complex I 9kDa subunit family. Mammalian complex I of mitochondrial respiratory chain is comprised of 45 different subunits. NDUFA4 protein has NADH dehydrogenase activity and oxidoreductase activity. NDUFA4 transfers electrons from NADH to the respiratory chain. The immediate electron acceptor for the NDUFA4 enzyme is assumed to be ubiquinone.

NADH Dehydrogenase Fe-S Protein 6 (NDUFS6) is a subunit of the NADH: ubiquinone oxidoreductase (complex I), which is the 1st enzyme complex in the electron transport chain of the mitochondria. This complex operates in the transfer of electrons from NADH to the respiratory chain. NDUFS6 is one of seven subunits in the iron-sulfur protein segment. DNA alterations in NDUFS6 are the cause for mitochondrial complex I deficiency, a disease which results in an extensive assortment of clinical disorders, like adult-onset neurodegenerative disorders and neonatal disease.

ACADS is a tetrameric mitochondrial flavoprotein, which is part of the acyl-CoA dehydrogenase family. ACADS catalyzes the first step of the mitochondrial fatty acid beta-oxidation pathway. Mutations in ACADS have been associated with Short Chain Acyl-CoA Dehydrogenase Deficiency.

AK4 belongs to the adenylate kinase family of enzymes. AK4 protein is restricted to the mitochondrial matrix. Adenylate kinases regulate the adenine and guanine nucleotide structures in a cell by catalyzing the reversible transfer of phosphate group among these nucleotides. Hereditary mutations which cause AK4 deficiencies in erythrocytes have been associated to hemolytic anemia.

TFB1M is a member of the methyltransferase superfamily. TFB1M is a dimethyltransferase which methylates mitochondrial 12S rRNA at the conserved stem loop. The TFB1M protein also is part of the basal mitochondrial transcription complex and is required for mitochondrial gene expression. TFB1M stimulates transcription independently of the methyltransferase activity.

ASS1 is involved in the urea cycle, which is a sequence of chemical reactions that is localized in liver cells. The urea cycle processes excess nitrogen that is generated as the body uses proteins. The surplus nitrogen is used to create a molecule called urea, which is excreted from the body in urine.

GMP synthase (GMPS) is involved in purine biosynthesis. GMPS, which is a homodimer, catalyzes the last step in the GMP synthesis pathway, specifically the ATP-dependent amination of XMP to GMP. GMPS is comprised of one GMP-binding domain and one glutamine amidotransferase type-1 domain through which it communicates its catalytic activity. GMPS is engaged in the de novo synthesis of nucleotides which are not only vital for DNA and RNA synthesis, but also supply GTP, which is involved in sevral cellular processes important for cell division. GMPS gene chromosomal translocations are linked with acute myeloid leukemias, suggesting a possible role for GMPS in carcinogenesis.

Transcription Factor B2, Mitochondrial (TFB2M) is an S-adenosyl-L-methionine-dependent methyltransferase which specifically dimethylates mitochondrial 12S rRNA at the conserved stem loop. In addition, TFB2M is essential for basal transcription of mitochondrial DNA, most likely via its interaction with POLRMT and TFAM. TFB2M promotes transcription independently of the methyltransferase activity. TFB2M like TFB1M, activates transcription of mitochondrial DNA more effectively, whilst having less methyltransferase activity.

NANS is a 359 amino acid protein that contains one AFP (antifreeze proteins)-like domain and functions in the biosynthesis of sialic acids. The ubiquitously expressed NANS enzymatically catalyzes the H2O-dependent formation of N-acetylneuraminic acid (Neu5Ac) and 2-keto-3-deoxy-D-glycero-D-galacto-nononic acid (KDN), both of which are sialic acids. NANS uses N-acetylmannosamine 6-phosphate as a substrate for Neu5Ac synthesis and mannose 6-phosphate as a substrate for KDN synthesis.

Mmitochondrial import receptor subunit TOMM20 homolog (TOMM20) is a member of the Tom20 family. The Tom machinery consists of import receptors for the initial binding of cytosolically synthesized preproteins and a general import pore (GIP) for the membrane translocation of various preproteins into the mitochondria. TOMM20 acts as the transit peptide receptor at the surface of the mitochondrion outer membrane and facilitates the movement of preproteins into the TOM40 translocation pore.

Phenylalanyl-tRNA synthetase 2 mitochondrial (FARS2) is a member of the class II aminoacyl- tRNA synthetase family. FARS2 is a mitochondrial matrix protein. FARS2 when acting as a monomer, catalyzes the ATP-dependent conversion of L-phenylalanine and tRNA (Phe) to L-phenlalanyltRNA (Phe), an event which is vital for proper translation and protein expression.

Porphobilinogen deaminase (HMBS) belongs to the hydroxymethylbilane synthase superfamily. HMBS is a cytoplasmic enzyme found in the heme synthesis pathway. HMBS is the 3rd enzyme of the heme biosynthetic pathway and catalyzes the head to tail condensation of 4 porphobilinogen molecules into the linear hydroxymethylbilane. HMBS gene mutations cause errors in pyrrole metabolism which in turn lead to the autosomal dominant disease acute intermittent porphyria.

Spermine synthase (SMS) is amember of the spermidine/spermine synthase family. SMS is an enzyme which converts spermidine into spermine. The SMS enzyme is essential for normal viability, growth and fertility involved in polyamine metabolism. Defects in the SMS gene are the cause of Snyder-Robinson syndrome (SRS), also known as X-linked mental retardation Snyder-Robinson type. SRS is categorized by moderate intellectual deficit, hypotonia, an unsteady gait, osteoporosis, kyphoscoliosis and facial asymmetry, its transmission is X-linked recessive.

6-PyruvoylTetrahydropterin Synthase is part of the family of lyases, specifically those carbon-oxygen lyases acting on phosphates. 6-PyruvoylTetrahydropterin Synthase catalyzes the elimination of inorganic triphosphate from dihydroneopterin triphosphate, which is the second and irreversible step in the biosynthesis of tetrahydrobiopterin from GTP. Tetrahydrobiopterin, is a necessary cofactor and regulator of a range of enzyme activities, including enzymes involved in serotonin biosynthesis and NO synthase activity. Mutations in 6-PyruvoylTetrahydropterin Synthase gene result in hyperphenylalaninemia.

PAPSS1 is a bifunctional enzyme with APS kinase and ATP sulfurylase activity. PAPSS1 facilitates two stages in the sulfate activation pathway, yielding 3'-phosphoadenylylsulfate (PAPS). Additionally, PAPSS1 takes part in the biosynthesis of sulfated L-selectin ligands in endothelial cells.

DNAJC19 is part of a complex involved in the ATP-dependent transport of transit peptide-containing proteins from the inner cell membrane to the mitochondrial matrix. DNAJC19 is a single-pass membrane protein which contains a J domain and is localized to the inner membrane of the mitochondrion. Expressed ubiquitously, DNAJC19 acts as a component of the mitochondrial DNAJC19 complex that is responsible for the ATP-dependent translocation of select proteins from the inner mitochondrial membrane to the mitochondrial matrix. Defects in the DNAJC19 gene are the cause of 3-methylglutaconic aciduria type 5 (MGA5), otherwise known as dilated cardiomyopathy with ataxia (DCMA).

MRPS25, a 28S subunit protein, is a member of the ribosomal protein S5P family. An equivalent pseudogene is located on chromosome 4.

MRPS25, a 28S subunit protein, is a member of the ribosomal protein S5P family. An equivalent pseudogene is located on chromosome 4.