| complement membrane attack complex | The assembly of complement plasma glycoproteins c5b, c6, c7, c8, and polymeric c9 as a group on biological membranes. The complex forms transmembrane channels which displace lipid molecules and other constituents, thus disrupting the phospholipid bilayer of target cells leading to cell lysis by osmotic leakage. The formation of the membrane attack complex is the terminal step in the complement cascade. (12 Dec 1998) |
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| complement pathway, alternative | The complement activation sequence initiated by the activation of complement factor c3, which is triggered by the interaction of microbial polysaccharides and properdin without participation of an antigen-antibody reaction. (12 Dec 1998) |
| complement pathway, classical | The sequential activation of complement, initiated by antigen-antibody complex and the binding of complement factor c1q to the fc region of the antibody. (12 Dec 1998) |
| complement system | A group of more than 20 serum proteins, some of which can be serially activated and participate in a cascade resulting in cell lysis. (05 Mar 2000) |
| complement unit | The smallest amount (highest dilution) of complement that will cause haemolysis of a unit of red blood cells in the presence of a haemolysin unit. Synonym: alexin unit. (05 Mar 2000) |
| component of complement | Any one of the nine distinct protein units (designated C1 through C9 and distributed in the a, b, and g electrophoretic partitions of normal serum) that effect the immunological activities long associated with complement. C1 is a complex of three subunits: C1q, C1r, and C1s. C1q (overbar indicates "active form") activates proenzyme C1r to C1r which activates C1s to C1s (also known as C1 esterase), which converts proenzyme C2 to C2b and produces C4b from C4. C2b combines with C4b to form "classical-complement-pathway C3/C5 convertase" (also known as C3 convertase, C5 convertase, and C42). This enzyme cleaves C3 to C3a and C3b, and C5 to yield C5a and C5b, as does "alternative-complement-pathway C3/C5 convertase" (also known as proenzyme factor B, properdin factor B, C3 proactivator, and heat-labile factor). Complement factor I (also known as C3b or C3b/C4b inactivator) inactivates C3b and C4b by a different proteolytic cleavage. Several autosomal recessive disorders have been identified in which one or more of the complement components have been deficient or completely absent. (05 Mar 2000) |
| heparin complement | The protein component of heparin in blood. (05 Mar 2000) |
| thyrotoxic complement-fixation factor | A form of thyrotoxin; an antigen found most readily in thyroid tissue from thyrotoxic individuals; known to be chemically and immunologically distinct from thyroglobulin, and fixes complement when combined with antibody related to the gamma-globulin fraction of serum. With the exception of extremely small concentrations, the antigen is rarely found in normal glands or in diseased glands that are not associated with thyrotoxicosis; it is probably an intracellular substance (possibly a constituent of the "microsomal fraction"), and does not contain iodine in significant quantity. Not related to the complement-fixation reaction occurring with serum in Hashimoto's disease, in which the antigen is thyroglobulin. (05 Mar 2000) |
| acetoacetyl-acyl carrier protein synthase | <enzyme> E coli enzyme, that catalyses condensation of malonyl-acyl carrier protein plus acetyl-acyl carrier protein; not inhibited by cerulenin Registry number: EC 2.3.1.- Synonym: acetoacetyl-acp synthase (26 Jun 1999) |
| acid soluble spore protein | <molecular biology> A DNA binding protein in the spores of some bacteria, thought to stabilise the DNA in an A configuration, so protecting it from cleavage by enzymes or UV light. (18 Nov 1997) |
| acute-phase protein | <haematology> These plasma proteins (in addition to fibrinogen) increase 25% or more in response to inflammation and injury are under direct control of interleukin-6 (IL-6) (hepatocyte-stimulating factor). Other proteins which increase are ceruloplasmin, C3 and C4 which increase 50% or more; alpha-1 acid glycoprotein, alpha-1 antitrypsin, haptoglobin and fibrinogen (the major determinant of viscosity 1 ) which increase two- to fourfold; C-reactive protein (CRP) and serum amyloid A which increase several hundred-fold. Despite long-held clinical opinion to the contrary, available data indicate that neither ESR nor measurement of specific acute-phase reactants are useful in excluding underlying infection or inflammation regardless of the pretest probability. These proteins are secreted into the blood in increased or decreased quantities by hepatocytes in response to trauma, inflammation, or disease. They can serve as inhibitors or mediators of the inflammatory processes. Certain acute-phase proteins have been used to diagnose and follow the course of diseases or as tumour markers. See also: amyloid, c-reactive protein, erythrocyte sedimentation rate, viscosity. (25 Jun 1999) |
| acyl-(acyl-carrier-protein)-phospholipid acyltransferase | <enzyme> Catalyses the formation of phosphatidylethanolamine from acyl-acyl carrier protein and 2-acyl-sn-glycero-3-phosphoethanolamine Registry number: EC 2.3.1.40 Synonym: 2-acyl-gpe acyltransferase, 2-acylglycerophosphoethanolamine acyltransferase (26 Jun 1999) |
| acyl-(acyl-carrier-protein)-UDP-N-acetylglucosamine acyltransferase | <enzyme> E coli enzyme involved in lipid a biosynthesis; uses beta-hydroxymyristoyl-acyl carrier protein to form udp-3-monoacyl-n-acetylglucosamine; amino acid sequence given in second source Registry number: EC 2.3.1.129 Synonym: udp-aguatransferase, lpxa protein, udp-n-acetylglucosamine-3-acyltransferase, udp-n-acetylglucosamine 3-o-acyltransferase, udp-3-o-(r-3-hydroxymyristoyl)glucosamine-n-acyltransferase, lpxd protein, fira gene product, fira protein (26 Jun 1999) |
| acyl carrier protein | <protein> A small (77 peptides long) protein which binds six other enzymes involved in fatty acid synthesis. It was first isolated in E. Coli bacteria. (09 Oct 1997) |
| acyl carrier protein acylase | <enzyme> From E coli Registry number: EC 2.3.1.- Synonym: acp acylase (26 Jun 1999) |