| complement 1q | <chemical> Subcomponent of complement 1 (c1) which recognises and binds to the heavy chain of IgG or IgM initiating the classical complement pathway. The interaction of c1q and immunoglobulin activates c1r and c1s. The activated c1r and c1s molecules are cleaved off the complex by c1-inhibitor, allowing the collagen-like region of c1q to become accessible for interaction with cell membrane c1q receptors. Chemical name: Complement C1q (12 Dec 1998) |
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| complement 1r | <enzyme> Subcomponent of complement 1 which, when activated by c1q, activates subcomponent c1s by proteolytic cleavage. Registry number: EC 3.4.21.41 (12 Dec 1998) |
| complement 1s | <enzyme> The activated form of complement 1 which has hydrolase activity. In the classical pathway, it splits first c4 and then c2 into active components, thereby generating a new enzyme referred to as eac142 or c42 or c3 convertase. Registry number: EC 3.4.21.42 (12 Dec 1998) |
| complement 2 | The third component in the complement reaction sequence. It is a beta-globulin with a molecular weight of 117,000, a serum concentration of 30 micrograms/ml and a sedimentation coefficient of 4. It activates c3. (12 Dec 1998) |
| complement 3 | The fourth component to attach in the complement reaction sequence. It is a beta-globulin with a sedimentation coefficient of 5.5, a molecular weight of 185,000 and a serum concentration of 1.3 micrograms/ml. Its fragments have anaphylatoxic, chemotactic, and histaminic action and affect smooth muscle. (12 Dec 1998) |
| complement 3a | <chemical> Smaller fragment formed when c3 convertase splits c3 into c3a and c3b. C3a is a 77-amino acid peptide that includes a carboxy-terminal arginine which is crucial for its biological activities. C3a causes symptoms of immediate hypersensitivity (anaphylaxis) including smooth muscle contraction, mast cell histamine release, and local inflammation. It is considered an anaphylatoxin along with c4a, c5a, and c5a des-arginine. Chemical name: Complement C3a (12 Dec 1998) |
| complement 3b | <chemical> The larger fragment formed when c3 convertase splits c3 into c3a and c3b. In both the classical and alternate pathway, c3b participates in immune adherence and enhances phagocytosis. It also forms a cellular intermediate which continues the complement process. In the alternate pathways, c3b initiates a positive feedback activation of c3pase. Chemical name: Complement C3b (12 Dec 1998) |
| complement 3b inactivators | Compounds which inhibit, antagonise, or inactivate complement 3b. A well-known inhibitor is a beta-globulin which cleaves c3b into inactive fragments c3c and c3d. C3bina plays a key role in the regulation of the complement system by blocking the cytolytic sequence and preventing recruitment of the properdin amplification loop. (12 Dec 1998) |
| complement 3c | <chemical> An inactivated form of complement 3b (c3b). Complement 3b is inactivated with the help of two regulatory factors, complement factor h and complement factor I. Complement factor h (c3b inactivator accelerator) makes c3b susceptible to the serine protease, complement factor I (formerly called kaf, c3binf, or enzyme 3b inactivator), to form ic3b. Then complement factor I and a trypsin-like proteolytic enzyme further cleave ic3b into c3c and c3dg. Chemical name: Complement C3c (12 Dec 1998) |
| complement 3 convertase | <enzyme> The enzyme which in both the classical and alternate complement pathways cleaves complement 3 into anaphylatoxin (c3a) and c3b. Registry number: EC 3.4.21.43 (12 Dec 1998) |
| complement 3d | <chemical> An inactivated fragment of complement 3b (c3b). Factor h makes c3b susceptible to factor I (formerly called kaf, c3binf, or enzyme 3b inactivator) to form ic3b. Then factor I and a trypsin-like proteolytic enzyme further cleave ic3b into c3c and c3dg. Serum proteases degrade c3dg into complement 3d (c3d) and c3g. Chemical name: Complement C3d (12 Dec 1998) |
| complement 3 nephritic factor | A magnesium-dependent IgG autoantibody found in serum of patients with chronic mesangioproliferative hypocomplementemic glomerulonephritis. It causes inactivation of c3 in the alternate pathway by cleaving c3 into two inactive fragments, c3c and c3d, instead of the normal c3b. (12 Dec 1998) |
| complement 4 | The second component to react in the complement sequence. It is a beta-globulin with a sedimentation coefficient of 18.7, a molecular weight of 240,000 and a serum concentration of 430 micrograms/ml. It is activated by complement 1 and serves as a receptor for c2. (12 Dec 1998) |
| complement 4a | <chemical> Smaller fragment formed when c1s splits c4 into c4a and c4b. As an anaphylatoxin, c4a causes symptoms of immediate hypersensitivity but it has weaker activity than c3a or c5a. Chemical name: Complement C4a (12 Dec 1998) |
| complement 4b | <chemical> Larger fragment formed when c1s splits c4 into c4a and c4b. C4b combines with c2b to form the activated c4b2b complex which is often called the classical pathway c3 convertase. Chemical name: Complement C4b (12 Dec 1998) |