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Prekallikrein
Prekallikrein (PK), also known as Fletcher factor, is an 85,000 Mr serine protease that complexes with high-molecular-weight kininogen. PK is the precursor of plasma kallikrein, which is a serine protease that activates kinins. PK is cleaved to produce kallikrein by activated Factor XII (Hageman factor). Structure Prekallikrein is homologous to factor XI, and similarly consists of four apple domains and a fifth, catalytic serine protease domain. The four apple domains create a disk-like platform around the base of the catalytic domain. However, unlike factor XI, prekallikrein does not form dimers. Prekallikrein is activated to form kallikrein by factor XII cleavage of a bond homologous to the corresponding bond cleaved during factor XI activation. Prekallikrein deficiency Hereditary deficiencies in PK are very rare. They can cause a prolonged APTT, which can be corrected by incubation of the patient’s plasma. Deficiencies in PK can also be acquired due to some disease st ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Coagulation System
Coagulation, also known as clotting, is the process by which blood changes from a liquid to a gel, forming a blood clot. It potentially results in hemostasis, the cessation of blood loss from a damaged vessel, followed by repair. The mechanism of coagulation involves activation, adhesion and aggregation of platelets, as well as deposition and maturation of fibrin. Coagulation begins almost instantly after an injury to the endothelium lining a blood vessel. Exposure of blood to the subendothelial space initiates two processes: changes in platelets, and the exposure of subendothelial tissue factor to plasma factor VII, which ultimately leads to cross-linked fibrin formation. Platelets immediately form a plug at the site of injury; this is called ''primary hemostasis. Secondary hemostasis'' occurs simultaneously: additional coagulation (clotting) factors beyond factor VII ( listed below) respond in a cascade to form fibrin strands, which strengthen the platelet plug. Disorders of c ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Kallikrein
Kallikreins are a subgroup of serine proteases, enzymes capable of cleaving peptide bonds in proteins. In humans, plasma kallikrein (encoded by ''KLKB1 gene'') has no known paralogue, while tissue kallikrein-related peptidases (''KLKs'') encode a family of fifteen closely related serine proteases. These genes are localised to chromosome 19q13, forming the largest contiguous cluster of proteases within the human genome. Kallikreins are responsible for the coordination of various physiological functions including blood pressure, semen liquefaction and skin desquamation. Occurrence In 1934, Eugen Werle reported finding a substance in the pancreas of humans and various animals in such large amounts that the pancreas could be taken for its site of origin. He named it kallikrein, by derivation from the Greek word for pancreas. Since then, similar enzymes have been found in the biological fluids of humans and other mammals, as well as in some snake venoms. Venom The caterpillar known ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Serine Protease
Serine proteases (or serine endopeptidases) are enzymes that cleave peptide bonds in proteins. Serine serves as the nucleophilic amino acid at the (enzyme's) active site. They are found ubiquitously in both eukaryotes and prokaryotes. Serine proteases fall into two broad categories based on their structure: chymotrypsin-like (trypsin-like) or subtilisin-like. Classification The MEROPS protease classification system counts 16 superfamilies (as of 2013) each containing many families. Each superfamily uses the catalytic triad or dyad in a different protein fold and so represent convergent evolution of the catalytic mechanism. The majority belong to the S1 family of the PA clan (superfamily) of proteases. For superfamilies, P: superfamily, containing a mixture of nucleophile class families, S: purely serine proteases. superfamily. Within each superfamily, families are designated by their catalytic nucleophile, (S: serine proteases). Substrate specificity Serine ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
High-molecular-weight Kininogen
High-molecular-weight kininogen (HMWK or HK) is a circulating plasma protein which participates in the initiation of blood coagulation, and in the generation of the vasodilator bradykinin via the kallikrein-kinin system. HMWK is inactive until it either adheres to binding proteins beneath an endothelium disrupted by injury, thereby initiating coagulation; or it binds to intact endothelial cells or platelets for functions other than coagulation. Other names In the past, HMWK has been called HMWK-kallikrein factor, Flaujeac factor (1975), Fitzgerald factor (1975), and Williams-Fitzgerald-Flaujeac factor, - the eponyms being for people first reported to have HMWK deficiency. Its current accepted name is to contrast it with ''low''-molecular-weight kininogen (LMWK) which has a similar function to HMWK in the tissue (as opposed to serum) kinin-kallikrein system. Structure and function HMWK is an alpha-globulin with six functional domains. It circulates as a single-chain 626 ami ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Factor XII
Coagulation factor XII, also known as Hageman factor, is a plasma protein. It is the zymogen form of factor XIIa, an enzyme () of the serine protease (or serine endopeptidase) class. In humans, factor XII is encoded by the ''F12'' gene. Structure Human Factor XII is 596 amino acids long and consists of two chains, the heavy chain (353 residues) and light chain (243 residues) held together by a disulfide bond. It is 80,000 daltons. Its heavy chain contains two fibronectin-type domains (type I and II), two epidermal growth factor-like domains, a kringle domain, and a proline-rich region, and its light chain contains the protease domain. The structure of the FnI-EGF-like tandem domain of coagulation factor XII has been solved by X-ray crystallography. Crystal structures of the FXII light chain has also been determined unbound (β-FXII) and bound (β-FXIIa) to inhibitors. Factor XII (FXII, Hageman factor) is a plasma glycoprotein of approximately 90 kDa molecular weight is part ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Homology (biology)
In biology, homology is similarity due to shared ancestry between a pair of structures or genes in different taxa. A common example of homologous structures is the forelimbs of vertebrates, where the wings of bats and birds, the arms of primates, the front flippers of whales and the forelegs of four-legged vertebrates like dogs and crocodiles are all derived from the same ancestral tetrapod structure. Evolutionary biology explains homologous structures adapted to different purposes as the result of descent with modification from a common ancestor. The term was first applied to biology in a non-evolutionary context by the anatomist Richard Owen in 1843. Homology was later explained by Charles Darwin's theory of evolution in 1859, but had been observed before this, from Aristotle onwards, and it was explicitly analysed by Pierre Belon in 1555. In developmental biology, organs that developed in the embryo in the same manner and from similar origins, such as from matching p ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Factor XI
Factor XI or plasma thromboplastin antecedent is the zymogen form of factor XIa, one of the enzymes of the coagulation cascade. Like many other coagulation factors, it is a serine protease. In humans, Factor XI is encoded by the ''F11'' gene. Function Factor XI (FXI) is produced by the liver and circulates as a homo-dimer in its inactive form. The plasma half-life of FXI is approximately 52 hours. The zymogen factor is activated into ''factor XIa'' by factor XIIa (FXIIa), thrombin, and FXIa itself; due to its activation by FXIIa, FXI is a member of the "contact pathway" (which includes HMWK, prekallikrein, factor XII, factor XI, and factor IX). Factor XIa activates factor IX by selectively cleaving arg-ala and arg- val peptide bonds. Factor IXa, in turn, forms a complex with Factor VIIIa (FIXa-FVIIIa) and activates factor X. Physiological inhibitors of factor XIa include protein Z-dependent protease inhibitor (ZPI, a member of the serine protease inhibitor/serpin class ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
PAN Domain
PAN protein domain, domains have significant functional versatility fulfilling diverse biology, biological roles by mediating protein-protein interaction, protein-protein and protein-carbohydrate interactions. These domains contain a Hairpin turn, hair-pin loop like structure, similar to that found in Inhibitor cystine knot, knottins but with a different pattern of disulfide bonds. It has been shown that the N-terminal domains of members of the plasminogen/hepatocyte growth factor family, the apple domains of the blood plasma, plasma prekallikrein/Factor XI, coagulation factor XI family, and domains of various nematode proteins belong to the same module superfamily, the PAN module. The PAN domain contains a conserved sequence, conserved core of three disulfide bridges. In some members of the family there is an additional fourth disulfide bridge that links the N-terminus, N- and C-terminus, C-termini of the domain. The apple domain, as well as other examples of the PAN domain, cons ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Factor XII
Coagulation factor XII, also known as Hageman factor, is a plasma protein. It is the zymogen form of factor XIIa, an enzyme () of the serine protease (or serine endopeptidase) class. In humans, factor XII is encoded by the ''F12'' gene. Structure Human Factor XII is 596 amino acids long and consists of two chains, the heavy chain (353 residues) and light chain (243 residues) held together by a disulfide bond. It is 80,000 daltons. Its heavy chain contains two fibronectin-type domains (type I and II), two epidermal growth factor-like domains, a kringle domain, and a proline-rich region, and its light chain contains the protease domain. The structure of the FnI-EGF-like tandem domain of coagulation factor XII has been solved by X-ray crystallography. Crystal structures of the FXII light chain has also been determined unbound (β-FXII) and bound (β-FXIIa) to inhibitors. Factor XII (FXII, Hageman factor) is a plasma glycoprotein of approximately 90 kDa molecular weight is part ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
APTT
The partial thromboplastin time (PTT), also known as the activated partial thromboplastin time (aPTT or APTT), is a blood test that characterizes coagulation of the blood. A historical name for this measure is the kaolin-cephalin clotting time (KCCT), reflecting kaolin and cephalin as materials historically used in the test. Apart from detecting abnormalities in blood clotting, partial thromboplastin time is also used to monitor the treatment effect of heparin, a widely prescribed drug that reduces blood's tendency to clot. The PTT measures the overall speed at which blood clots form by means of two consecutive series of biochemical reactions known as the ''intrinsic'' pathway and common pathway of coagulation. The PTT indirectly measures action of the following coagulation factors: I (fibrinogen), II (prothrombin), V (proaccelerin), VIII (anti-hemophilic factor), X (Stuart–Prower factor), XI (plasma thromboplastin antecedent), and XII (Hageman factor). The PTT is of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Angioedema
Angioedema is an area of swelling ( edema) of the lower layer of skin and tissue just under the skin or mucous membranes. The swelling may occur in the face, tongue, larynx, abdomen, or arms and legs. Often it is associated with hives, which are swelling within the upper skin. Onset is typically over minutes to hours. The underlying mechanism typically involves histamine or bradykinin. The version related to histamine is due to an allergic reaction to agents such as insect bites, foods, or medications. The version related to bradykinin may occur due to an inherited problem known as C1 esterase inhibitor deficiency, medications known as angiotensin-converting enzyme inhibitors, or a lymphoproliferative disorder. Treatment to protect the airway may include intubation or cricothyroidotomy. Histamine-related angioedema can be treated with antihistamines, corticosteroids, and epinephrine. In those with bradykinin-related disease a C1 esterase inhibitor, ecallantide, or icati ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
