| membrane attack complex | <immunology> A term originally used to refer to the heat labile factor in serum that causes immune cytolysis, the lysis of antibody coated cells and now referring to the entire functionally related system comprising at least 20 distinct serum proteins that is the effector not only of immune cytolysis but also of other biologic functions. Complement activation occurs by two different sequences, the classic and alternative pathways. The proteins of the classic pathway are termed components of complement and are designated by the symbols C1 through C9. C1 is a calcium dependent complex of three distinct proteins C1q, C1r and C1s. The proteins of the alternative pathway (collectively referred to as the properdin system) and complement regulatory proteins are known by semisystematic or trivial names. Fragments resulting from proteolytic cleavage of complement proteins are designated with lower case letter suffixes, for example, C3a. Inactivated fragments may be designated with the suffix i, for example C3bi. Activated components or complexes with biological activity are designated by a bar over the symbol for example C1 or C4b, 2a. The classic pathway is activated by the binding of C1 to classic pathway activators, primarily antigen-antibody complexes containing IgM, IgG1, IgG3, C1q binds to a single IgM molecule or two adjacent IgG molecules. The alternative pathway can be activated by IgA immune complexes and also by nonimmunologic materials including bacterial endotoxins, microbial polysaccharides and cell walls. Activation of the classic pathway triggers an enzymatic cascade involving C1, C4, C2 and C3, activation of the alternative pathway triggers a cascade involving C3 and factors B, D and P. Both result in the cleavage of C5 and the formation of the membrane attack complex. Complement activation also results in the formation of many biologically active complement fragments that act as anaphylatoxins, opsonins or chemotactic factors. (05 Jan 1998) |
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| charge transfer complex | A complex between two organic molecules in which an electron from one (the donor) is transferred to the other (the acceptor), becoming generally distributed throughout the latter; subsequent transfer of a hydrogen atom completes the reduction of the acceptor; such complex's are generally highly coloured and may be so observed, a network of hydrogen bridges at the catalytic centre of certain proteases. Synonym: charge transfer system. (05 Mar 2000) |
| periodontitis complex | Vertical resorption of the alveolar process with pockets of uneven depth on adjacent teeth, and with traumatic occlusion as a factor. (05 Mar 2000) |
| ribosome-lamella complex | A cylindrical cytoplasmic inclusion composed of concentrically arranged sheets of membranes alternating with rows of ribosomes; characteristic of the hairy cell in leukaemic reticuloendotheliosis. (05 Mar 2000) |
| persecution complex | A feeling that others have evil designs against one's well-being. (05 Mar 2000) |
| met repressor operator complex | Repressor protein, 104 residues, product of the metJ gene, which regulates methionine biosynthesis in E. Coli. Dimeric molecules bind to adjacent sites 8 base pairs apart on the DNA, sequence recognition is by interaction between antiparallel strands of protein and the major groove of the B form DNA duplex. (18 Nov 1997) |
| Meyenburg's complex | Clusters of small bile ducts occurring in polycystic livers, separate from the portal areas. (05 Mar 2000) |
| Michaelis complex | Binary complex of an enzyme. (05 Mar 2000) |
| monophasic complex | A complex in the electrocardiogram that is entirely negative or entirely positive. (05 Mar 2000) |
| mother superior complex | The tendency of a psychotherapist to play a mothering role to the detriment of the therapeutic process. (05 Mar 2000) |
| 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) |
| complex | Complicated, not simple. Origin: L. Complexus = woven together, encompassing (18 Nov 1997) |
| complex carbohydrate | <biochemistry> The combination of carbohydrates and fibre. (05 Jan 1998) |
| complex closure | <surgery, technique> A sutural repair that may involve multi-layered closure, debridement or advanced tissue repair (plasty). (05 Jan 1998) |
| complex febrile convulsion | A febrile convulsion that is prolonged (greater than 15 minutes' duration) or is associated with focal neurological deficits. (05 Mar 2000) |