Abortive infection

Acanthus

B-gene products, also glycosyl-transferases, can then add N-acetyl galactosamine or galactose to produce the A or B-antigens, respectively. Antibodies to the ABO-antigens occur naturally and make this an important set of antigens for blood transfusion. Transfusion of mismatched blood with surface red cell antigens that elicit a response leads to a transfusion reaction. The natural antibodies are usually IgM. See Rhesus, Kell, Duffy and MN blood group antigens.

abortive infection Viral infection of a cell in which the virus fails to replicate fully or produces defective progeny. Since part of the viral replicative cycle occurs, its effect on the host can still be cytopathogenic.

abortive transformation Temporary transformation of a cell by a virus that fails to integrate into the host DNA.

ABP See actin-binding proteins. A useful web resource, the Encyclopedia of Actin-Binding Proteins has been put together by S. Maclver of Edinburgh University.

Abplp An actin-binding protein originally from yeast and associated with the membrane. Has an ADF domain and an SH3 domain. Mammalian homologues are thought to have a role in endocytosis. Abplp binds actin through a region homologous to ADF/cofilin and to dynamin through the SH3 domain.

ABP-50 Actin-binding protein (50 kDa) from Dictyostelium that cross-links actin filaments into tight bundles. Identical to elongation factor EF-la. Calcium insensitive; localized near cell periphery and in protrusions from moving cells.

ABP-67 Early name for fimbrin. In yeast encoded by SAC6 gene, mutations which lead to disruption of the actin cytoskeleton.

ABP-120 Dictyostelium gelation factor Actin-binding protein (857 amino acids; 92 kDa) from Dictyostelium. A small rod-shaped molecule (35-40 nm long), dimeric, capable of cross-linking filaments. Has strong sequence similarities with ABP-280.

ABP-280 Actin-binding protein (2647 amino acids; 280 kDa) originally isolated from Dictyostelium, but very similar to filamin from other sources. A long rod-shaped phosphoprotein (80 nm long) present in the periphery of the cytoplasm, dimeric, with the two monomers associated end-to-end making a very long cross-linker of microfilaments. Associates with the third cytoplasmic loop of dopamine D(2) and D(3) receptors, but not with D(4) receptors. Has actin-binding domain similar to that in ABP-120, spectrin, filamin, alpha-actinin and fimbrin; also has binding site for platelet von Willebrand factor.

abrin Toxic lectin from seeds of Abrusprecatorius (jequir-ity bean) that has a binding site for galactose and related residues in carbohydrate but, because it is monovalent, is not an agglutinin for erythrocytes. Abrin-a A-chain (ABRaA) has N-glycosylase activity towards eukaryotic 28S rRNA.

abscess A cavity within a tissue occupied by pus (chiefly composed of degenerating inflammatory cells), generally caused by bacteria that resist killing by phagocytes.

abscisic acid A growth-inhibiting plant hormone found in vascular plants. Originally believed to be important in abscission (leaf fall), now known to be involved in a number of growth and developmental processes in plants, including, in some circumstances, growth promotion. Primary plant hormone that mediates responses to stress. Downstream signalling through cyclic ADP-ribose as a second messenger.

absolute lethal concentration, LC100 Lowest concentration of a substance that kills 100% of test organisms or species under defined conditions. This value is dependent on the number of organisms used in its assessment.

absorption coefficient 1. Any of four different coefficients that indicate the ability of a substance to absorb electromagnetic radiation. Absorbance is defined as the logarithm of the ratio of incident and transmitted intensity, and thus it is necessary to know the base of the logarithm used. Scattering and reflectance are generally ignored when dealing with solutions. 2. Ratio of the amount of a substance absorbed (uptake) to the administered quantity (intake).

absorption spectrum Spectrum of wavelengths of electromagnetic radiation (usually visible and UV light) absorbed by a substance. Absorption is determined by existence of atoms that can be excited from their ground state to an excited state by absorption of energy carried by a photon at that particular wavelength.

ABTS 2,2'-Azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) Compound that will produce a water-soluble, green-coloured product upon reaction with horseradish peroxidase; used in enzyme-linked immunoassays. It is light sensitive and must be kept in the dark both as a stock solution and as a working solution.

abzyme A catalytic antibody, one that has enzymic activity. Catalytic antibodies have two distinct advantages, they can be selected to catalyse a reaction that is not catalysed by endogenous enzymes, and, to minimize immunogenicity, humanization is possible.

acamprosate Calcium acetylaminopropane sulfonate A synthetic compound with a chemical structure similar to that of the endogenous amino acid homotaurine, which is a structural analogue of the amino acid neurotransmitter ^-aminobutyric acid and the amino acid neuromodulator taurine. A drug thought to be beneficial in maintaining abstinence in alcohol-dependent patients although the mechanism of action is unclear.

Acanthamoeba Soil amoebae 20-30 Jim in diameter that can be grown under axenic conditions and have been extensively used in biochemical studies of cell motility. They have been isolated from cultures of monkey kidney cells, and are pathogenic when injected into mice or monkeys.

acanthocyte Cell with projecting spikes; most commonly applied to erythrocytes, where the condition may be caused naturally by abetalipoproteinaemia or experimentally by manipulating the lipid composition of the plasma membrane.

acanthocytosis Condition in which red cells of the blood show spiky deformation; symptomatic of abetalipoproteinaemia. See acanthocyte.

acanthosis nigricans A rare disease characterized by pigmentation and warty growths on the skin. Often associated with cancer of the stomach or uterus.

acanthosome 1. Spinous membranous organelle found in skin fibroblasts from nude mice as a result of chronic ultraviolet irradiation. 2. Sometimes used as a synonym for coated vesicle (should be avoided).

Acanthus Genus of spiny-leaved Mediterranean plants.

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