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Translocase of Outer Mitochondrial Membrane 34 (TOMM34) which is found in the cytoplasm and sometimes associated with the outer mitochondrial membrane is involved in the import of precursor proteins into mitochondria. TOMM34 has a chaperone-like activity, binding the mature portion of unfolded proteins and aiding their import into mitochondria. TOMM34 has a weak ATPase activity and contains 6 TPR repeats.

NDUFS4 is a subunit of the mitochondrial membrane respiratory chain NADH dehydrogenase (Complex I), the primary multi-subunit enzyme complex of the mitochondrial respiratory chain. Complex I is involved in cellular ATP production, the main source of energy for numerous vital processes in living cells. NDUFS4 removes electrons from NADH and passes them by a series of diverse protein-coupled redox centers to the electron acceptor ubiquinone. NDUFS4 presents a hotspot of mutations in the genetic apparatus of oxidative phosphorylation and the correct assembly of the subunit it encodes is essential for completion of the assembly of complex I.

NADH Dehydrogenase Flavoprotein 2 (NDUFV2) is a 24 kDa Core subunit of the mitochondrial membrane respiratory chain NADH dehydrogenase (Complex I) which is a part of the minimal assembly required for catalysisthe. NDUFV2 is aslo involved in electron transfer. Mutations in NDUFV2 are implicated in Parkinson's disease, bipolar disorder, schizophrenia, and have been discovered in one case of early onset hypertrophic cardiomyopathy and encephalopathy.

NDUFS2 is a core subunit of the mitochondrial membrane respiratory chain NADH dehydrogenase (Complex I) which is a part of the minimal assembly required for catalysis. Complex I takes part in the transfer of electrons from NADH to the respiratory chain. Histidine NADH Dehydrogenase Fe-S Protein 2 (NDUFS2) is required for catalytic activity. Imperfections in NDUFS2 are the source of complex I mitochondrial respiratory chain deficiency, which is characterized by many symptoms including liver failure, cardiomyopathy and neurodegeneration.

Adenylate kinases play a role in regulating the adenine nucleotide composition within a cell by catalyzing the reversible transfer of phosphate groups among adenine nucleotides. There are 3 types of adenylate kinase isozymes, AK1, AK2, and AK3 in vertebrates. Expression of these isozymes are tissue-specific and developmentally regulated. AK2 is localized in the mitochondrial intermembrane space and is involved in apoptosis. AK2 is mutated in individuals with reticular dysgenesis.

NUDT9 is a member of a superfamily of Nudix hydrolases. NUDT9 functions as a highly specific adenosine diphosphate ribose pyrophosphatase which hydrolyzes ADP ribose to AMP and ribose 5'-phosphate. In addition, NUDT9 may be involved in the regulation of the menstrual cycle and may be related to the proliferation of glandular cells in the human endometrium.

Methionine sulfoxide reductase A (MSRA) is a member of the MsrA Met sulfoxide reductase family. The MSRA enzyme has a vital function as a repair enzyme for proteins which have been inactivated by oxidation. MSRA catalyzes the reversible oxidation-reduction of methionine sulfoxide in proteins to methionine. The three substrates of the MSRA enzyme are peptide-L-methionine, thioredoxin disulfide, and H2O, while its 2 products are peptide-L-methionine (R)-S-oxide and thioredoxin. The MSRA protein is ubiquitous and extremely conserved. Human and animal studies have shown the ultimate levels of expression in kidney and nervous tissue.

SMCP is a protein-coding gene. SMCP localizes to the capsule linked with the mitochondrial outer membranes and assumed to function in the organization and stabilization of the helical structure of the sperm's mitochondrial sheath. Sperm mitochondria vary in morphology and subcellular localization from those of somatic cells. They are elongated, flattened, and arranged circumferentially construct a helical coiled sheath in the midpiece of the sperm flagellum. Diseases associated with SMCP include middle ear disease, and hard palate cancer.

Aspartoacylase is a homodimer which catalyzes the deacetylation of N-acetylaspartic acid (NAA) (a protein whose hydrolysis is crucial to maintenance of intact white matter) to generate acetate and L-aspartate. Aspartoacylase (ASPA) is expressed in the liver, lung and kidney tissue, as well as in the skeletal muscle and in cerebral white matter. NAA is ample in the brain where hydrolysis by aspartoacylase is believed to aid maintain white matter. In other tissues ASPA functions as a scavenger of NAA from body fluids. ASPA gene mutations cause Canavan disease (CAND or spongy degeneration of the brain).

Mitochondrial Ribosome Recycling Factor (MRRF) is a member of the RRF family. MRRF attaches to the large ribosomal subunit in the cleft which has a peptidyl transferase center. MRRF controls the release of ribosome from messenger RNA at the termination of protein biosynthesis. Also, it may intensify the efficacy of translation by recycling ribosome from one round of translation to another.

GNPNAT1 is a member of the GNA1 subfamily of the larger acetyltransferase family of proteins. GNPNAT1 is limited to the Golgi apparatus and the endosome. GNPNAT1 is vital for UDPGlcNAc biosynthesis pathway. GNPNAT1 catalyzes the synthesis of GlcNAc6P from AcCoA and GlcN6P, a step in the UDP-GlcNAc6P formation pathway.

Ornithine aminotransferase is a key enzyme in the pathway that converts arginine and ornithine into the major excitatory and inhibitory neurotransmitters glutamate and GABA. Ornithine aminotransferase (OAT) is a 49kDa nucleus-encoded protein imported into mitochondria to give the mature 48kDa OAT polypeptide. It is found in humans, animals, insects, plants and microorganisms. The OAT has a sex-differential expression in the mouse kidney. OAT plays central physiological roles in amino acid metabolism. OAT shows a large structural and mechanistic similarity to other enzymes from the subgroup III of aminotransferases that transfer an amino group from a carbon atom which doesn’t carry a carboxyl function. OAT is vital for nitrogen recycling from arginine but not for the stress-induced proline accumulation. OAT enzyme deficiency causes the autosomal recessive eye disease Gyrate Atrophy.

Cytochrome b5 reductase 1 (CYB5R1) is a part of the flavoprotein pyridine nucleotide cytochrome reductase family. CYB5R1 is engaged in desaturation and elongation of fatty acids, cholesterol biosynthesis, drug metabolism, and, in erythrocyte, methemoglobin decrease.

Glutamyl-TRNA Amidotransferase, Subunit C also known as GATC allows the formation of properly charged Gln-tRNA(Gln) through the transamidation of misacylated Glu-tRNA(Gln) in the mitochondria. The reaction occurs in the attendance of glutamine and ATP through an activated gamma-phospho-Glu-tRNA(Gln). In addition, GATC is subunit of the heterotrimeric GatCAB amidotransferase (AdT) complex, composed of A (QRSL1), B (PET112) and C (GATC) subunits.

Mammalian mitochondrial ribosomal proteins are encoded by nuclear genes and assist in protein synthesis within the mitochondrion. Mitochondrial ribosomes (mitoribosomes) consist of a small 28S subunit and a large 39S subunit (MRPL13 is a 39S subunit protein) and have an estimated 75% protein to rRNA composition compared to prokaryotic ribosomes, where this ratio is reversed. An additional difference between mammalian mitoribosomes and prokaryotic ribosomes is that the second contain a 5S rRNA. Among various species, the proteins comprising the mitoribosome differ greatly in sequence, and sometimes in biochemical properties, which prevents easy recognition by sequence homology.

HPRT1 has a main part in the generation of purine nucleotides through the purine salvage pathway. HPRT1 primarily functions to salvage purines from degraded DNA to renewed purine synthesis. Therefore, it performs as a catalyst in the reaction between guanine and phosphoribosyl pyrophosphate to form GMP.

GPD2 (Mitochondrial glycerol-3-phosphate dehydrogenase) is a Ca2+-sensitive, FAD-binding protein, which is located on the outer surface of the inner mitochondrial membrane. Two isoforms have been identified for mGPD: Isoform 1 is comprised of 727 a.a. residues, while isoform 2 lacks 126 a.a. residues of the N-terminus. GPD2 catalyses the oxidation of glycerol-3-phosphate to DHAP (dihydroxyacetone phosphate) with associated reduction of the enzyme-bound FAD. GPD2 is a testis-specific promoter of mitochondrial GPDH. GPD2 along with a cytosolic NAD-linked GPD forms the glycerol phosphate shuttle that uses the interconversion of G-3-P and DHAP to transfer reducing equivalents into mitochondria, which results in the reoxidation of NADH produced during glycolysis.
GPD2 deficiency contributes to the impairment of glucose-stimulated INS discharge in a number of animal models of non-INS dependent diabetes mellitus. GPD2 up-regulation as a result of a highly glycolytic environment contributes to the general increase in ROS generation and may lead to the progression of prostate cancer.

DARS uses a 2 step reaction to catalyze the specific attachment of an amino acid to its cognate tRNA: the amino acid (AA) is first activated by ATP to form AA-AMP and then transferred to the acceptor end of the tRNA.

GSK3B is a serine-threonine kinase that belongs to the glycogen synthase kinase subfamily. GSK3B is involved in energy metabolism, neuronal cell development, and body pattern formation. Polymorphisms in the GSK3B gene have been implicated in modifying risk of Parkinson disease, and studies in mice show that overexpression of the GSK3B gene may be significant to the pathogenesis of Alzheimer disease.

SOD2 is part of the iron/manganese superoxide dismutase family. It encodes a mitochondrial protein that forms a homotetramer and binds one manganese ion per subunit. SOD2 binds to the superoxide byproducts of oxidative phosphorylation and converts them to hydrogen peroxide and diatomic oxygen. Mutations in SOD2 gene have been associated with idiopathic cardiomyopathy (IDC), premature aging, sporadic motor neuron disease, and cancer. SOD2 destroys radicals which are usually produced within the cells and which are toxic to biological systems.

Isocitrate Dehydrogenase is an enzyme of the oxidoreductase class that catalyzes the conversion of isocitrate and NAD+ to yield 2-ketoglutarate, carbon dioxide, and NADH. It occurs in cell mitochondria. The enzyme requires Mg2+, Mn2+; it is activated by ADP, citrate, and Ca2+, and inhibited by NADH, NADPH, and ATP. The reaction is the key rate-limiting step of the citric acid (tricarboxylic) cycle.

PRPS1 catalyzes the synthesis of phosphoribosylpyrophosphate (PRPP) that is essential for nucleotide synthesis. PRPS1 catalyzes the phosphoribosylation of ribose 5-phosphate to 5-phosphoribosyl-1-pyrophosphate, which is essential for purine metabolism and nucleotide biosynthesis. Defects in PRPS1 result in phosphoribosylpyrophosphate synthetase superactivity, Charcot-Marie-Tooth disease X-linked recessive type 5 and Arts Syndrome.

Sulfite oxidase, also known as SUOX is a homodimeric protein localized to the intermembrane space of mitochondria. Each subunit includes a heme domain as well as a molybdopterin-binding domain. The SUOX enzyme catalyzes the oxidation of sulfite to sulfate, the last reaction in the oxidative degradation of the sulfur amino acids cysteine and methionine. In addition, the deficiency of SUOX results in neurological abnormalities which are often fatal at an early age.

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).