A transmembrane protein is a type of integral membrane protein that spans the entirety of the cell membrane. Many transmembrane proteins function as gateways to permit the transport of specific substances across the membrane. They frequently undergo significant conformational changes to move a substance through the membrane. They are usually highly hydrophobic and aggregate and precipitate in water. They require detergents or nonpolar solvents for extraction, although some of them (beta-barrels) can be also extracted using denaturing agents.
DNA primase is an enzyme involved in the replication of DNA and is a type of RNA polymerase. Primase catalyzes the synthesis of a short RNA segment called a primer complementary to a ssDNA template. After this elongation, the RNA piece is removed by a 5' to 3' exonuclease and refilled with DNA.
Ribonucleotide reductase (RNR), also known as ribonucleoside diphosphate reductase, is an enzyme that catalyzes the formation of deoxyribonucleotides from ribonucleotides. It catalyzes this formation by removing the 2'-hydroxyl group of the ribose ring of nucleoside diphosphates. This reduction produces deoxyribonucleotides. Deoxyribonucleotides in turn are used in the synthesis of DNA. The reaction catalyzed by RNR is strictly conserved in all living organisms. Furthermore, RNR plays a critical role in regulating the total rate of DNA synthesis so that DNA to cell mass is maintained at a constant ratio during cell division and DNA repair. A somewhat unusual feature of the RNR enzyme is that it catalyzes a reaction that proceeds via a free radical mechanism of action. The substrates for RNR are ADP, GDP, CDP and UDP. dTDP is synthesized by another enzyme from dTMP.
The Rossmann fold is a tertiary fold found in proteins that bind nucleotides, such as enzyme cofactors FAD, NAD+, and NADP+. This fold is composed of alternating beta strands and alpha helical segments where the beta strands are hydrogen bonded to each other forming an extended beta sheet and the alpha helices surround both faces of the sheet to produce a three-layered sandwich. The classical Rossmann fold contains six beta strands whereas Rossmann-like folds, sometimes referred to as Rossmannoid folds, contain only five strands. The initial beta-alpha-beta (bab) fold is the most conserved segment of the Rossmann fold. The motif is named after Michael Rossmann who first noticed this structural motif in the enzyme lactate dehydrogenase in 1970 and who later observed that this was a frequently occurring motif in nucleotide binding proteins.
Thioredoxin reductases are enzymes that reduce thioredoxin (Trx). Two classes of thioredoxin reductase have been identified: one class in bacteria and some eukaryotes and one in animals. In bacteria TrxR also catalyzes the reduction of glutaredoxin like proteins known as NrdH. Both classes are flavoproteins which function as homodimers. Each monomer contains a FAD prosthetic group, a NADPH binding domain, and an active site containing a redox-active disulfide bond.
This is a list of topics in molecular biology. See also index of biochemistry articles.
Biliverdin reductase (BVR) is an enzyme found in all tissues under normal conditions, but especially in reticulo-macrophages of the liver and spleen. BVR facilitates the conversion of biliverdin to bilirubin via the reduction of a double bond between the second and third pyrrole ring into a single bond.
A DNA clamp, also known as a sliding clamp, is a protein complex that serves as a processivity-promoting factor in DNA replication. As a critical component of the DNA polymerase III holoenzyme, the clamp protein binds DNA polymerase and prevents this enzyme from dissociating from the template DNA strand. The clamp-polymerase protein–protein interactions are stronger and more specific than the direct interactions between the polymerase and the template DNA strand; because one of the rate-limiting steps in the DNA synthesis reaction is the association of the polymerase with the DNA template, the presence of the sliding clamp dramatically increases the number of nucleotides that the polymerase can add to the growing strand per association event. The presence of the DNA clamp can increase the rate of DNA synthesis up to 1,000-fold compared with a nonprocessive polymerase.
In molecular biology, the protein domain Saccharopine dehydrogenase (SDH), also named Saccharopine reductase, is an enzyme involved in the metabolism of the amino acid lysine, via an intermediate substance called saccharopine. The Saccharopine dehydrogenase enzyme can be classified under EC 1.5.1.7, EC 1.5.1.8, EC 1.5.1.9, and EC 1.5.1.10. It has an important function in lysine metabolism and catalyses a reaction in the alpha-Aminoadipic acid pathway. This pathway is unique to fungal organisms therefore, this molecule could be useful in the search for new antibiotics. This protein family also includes saccharopine dehydrogenase and homospermidine synthase. It is found in prokaryotes, eukaryotes and archaea.
The enzyme chorismate synthase catalyzes the chemical reaction
Aldo-keto reductase family 1 member C3 (AKR1C3), also known as 17β-hydroxysteroid dehydrogenase type 5 or 3α-hydroxysteroid dehydrogenase type 2 (3α-HSD2) is a steroidogenic enzyme that in humans is encoded by the AKR1C3 gene.
Aldo-keto reductase family 1 member C1 also known as 20α-hydroxysteroid dehydrogenase, 3α-hydroxysteroid dehydrogenase, and dihydrodiol dehydrogenase 1/2 is an enzyme that in humans is encoded by the AKR1C1 gene.
Adrenodoxin reductase, was first isolated from bovine adrenal cortex where it functions as the first enzyme in the mitochondrial P450 systems that catalyze essential steps in steroid hormone biosynthesis. Examination of complete genome sequences revealed that adrenodoxin reductase gene is present in most metazoans and prokaryotes.
The aldo-keto reductase family is a family of proteins that are subdivided into 16 categories; these include a number of related monomeric NADPH-dependent oxidoreductases, such as aldehyde reductase, aldose reductase, prostaglandin F synthase, xylose reductase, rho crystallin, and many others.
Tus, also known as terminus utilization substance, is a protein that binds to terminator sequences and acts as a counter-helicase when it comes in contact with an advancing helicase. The bound Tus protein effectively halts DNA polymerase movement. Tus helps end DNA replication in prokaryotes.
S-Adenosylmethionine synthetase, also known as methionine adenosyltransferase (MAT), is an enzyme that creates S-adenosylmethionine by reacting methionine and ATP.
In molecular biology, the protein domain SAND is named after a range of proteins in the protein family: Sp100, AIRE-1, NucP41/75, DEAF-1. It is localised in the cell nucleus and has an important function in chromatin-dependent transcriptional control. It is found solely in eukaryotes.
In molecular biology the SeqA protein is found in bacteria and archaea. The function of this protein is highly important in DNA replication. The protein negatively regulates the initiation of DNA replication at the origin of replication, in Escherichia coli, OriC. Additionally the protein plays a further role in sequestration. The importance of this protein is vital, without its help in DNA replication, cell division and other crucial processes could not occur. This protein domain is thought to be part of a much larger protein complex which includes other proteins such as SeqB.
5β-Reductase, or Δ4-3-oxosteroid 5β-reductase (EC 1.3.1.3, 3-oxo-Δ4-steroid 5β-reductase, androstenedione 5β-reductase, cholestenone 5β-reductase, cortisone 5β-reductase, cortisone Δ4-5β-reductase, steroid 5β-reductase, testosterone 5β-reductase, Δ4-3-ketosteroid 5β-reductase, Δ4-5β-reductase, Δ4-hydrogenase, 4,5β-dihydrocortisone:NADP+ Δ4-oxidoreductase, 3-oxo-5β-steroid:NADP+ Δ4-oxidoreductase) is an enzyme with systematic name 5β-cholestan-3-one:NADP+ 4,5-oxidoreductase. This enzyme catalyses the following chemical reaction
Biliverdin reductase B is a protein that in humans is encoded by the BLVRB gene.
