| on-off phenomenon | A state in the treatment of Parkinson's disease by l-dopa, in which there is a rapid fluctuation of akinetic (off) and choreoathetotic (on) movements. (05 Mar 2000) |
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| ordered on-random off mechanism | A scheme for substrate binding and product release for multisubstrate enzymes; for a two-substrate two-product enzyme with this mechanism, the individuals have to bind to the enzyme in a distinct order; however, once the products are formed they may dissociate from the enzyme in either order. It has been suggested that pyruvate kinase has such a mechanism. The random on-ordered off mechanism is simply the reverse of this mechanism. (05 Mar 2000) |
| acetyl reduction assay | <investigation> A technique for measuring the nitrogen fixation activity in photosynthetic organisms. It uses a flame ionisation detector and a gas chromatography apparatus to determine the reduction of acetylene to ethylene by the enzyme nitrogenase. (06 May 1997) |
| Ames assay | <procedure> One of a number of procedures used to test substances for likely ability to cause cancer that combines the use of animal tissue to generate active metabolites of the substance with a test for mutagenicity in bacteria. (18 Nov 1997) |
| antibiotic assay | <investigation> A test to determine how sensitive a bacterial or fungal strain is to arange of antibiotics bymeasuring the microbes' ability to grow in astandard dilution of each chemical. (09 Oct 1997) |
| assay | <procedure> The determination of the amount of a particular constituent of a mixture or of the biological or pharmacological potency of a drug. (10 May 1997) |
| bandshift assay | <investigation> An assay for proteins, such as transcription factors, that bind specific DNA sequences. A labelled oligonucleotide corresponding to the recognition sequence is incubated with an appropriate nuclear protein extract and run on a nondenaturing acrylamide gel. Oligonucleotides that have been bound by proteins are retarded relative to those that are unbound. (18 Nov 1997) |
| biological assay | <technique> Once a pharmaceutical protein is isolated from the cells in which it was grown, researchers perform tests to measure the protein's biological activity. It must maintain a certain minimal level of biological activity to be used for animal or clinical testing or, later, for market. Researchers also test to confirm that the isolated protein is identical to the desired protein. (21 Mar 1998) |
| radioimmunoprecipitation assay | Sensitive assay using radiolabelled antigens to detect specific antibodies in serum. The antigens are allowed to react with the serum and then precipitated using a special reagent such as protein a sepharose beads. The bound radiolabelled immunoprecipitate is then commonly analyzed by gel electrophoresis. Radioimmunoprecipitation assay (ripa) is often used as a confirmatory test for diagnosing the presence of HIV antibodies. (12 Dec 1998) |
| radioligand assay | <radiobiology> Quantitative determination of receptor (binding) proteins in body fluids or tissue using radioactively labelled binding reagents (e.g., antibodies, intracellular receptors, plasma binders). (12 Dec 1998) |
| radioreceptor assay | A competitive binding assay in which the binder is a membrane or tissue receptor rather than an antibody. (05 Mar 2000) |
| Raji cell radioimmune assay | For immune complexes; a procedure by which immune complexes adsorbed from a test serum by a standard preparation of lymphoblastoid (Raji) cells are assayed by the capacity to bind 125I-labelled antibody to immunoglobulin. (05 Mar 2000) |
| gel retardation assay | A lab technique used to find out if there are proteins binding a fragment of DNA (in a DNA-protein complex) by watching how fast the DNA fragment moves through an electric field and seeing whether it moves slower when a particular protein is also present. (09 Oct 1997) |
| checkerboard assay | <procedure> Variant of the Boyden chamber assay for leucocyte chemotaxis introduced by Zigmond. By testing different concentrations of putative chemotactic factor in nongradient conditions, it is possible to calculate the enhancement of movement expected due simply to chemokinesis and to compare this with the distances moved in positive and negative gradients. Good experimental design thus allows chemotaxis to be distinguished from chemokinesis. (21 May 1997) |
| chloramphenicol acetyltransferase assay | <investigation> A lab technique used to determine whether a given fragment of DNA has a promoter on it to encourage transcription to occur, by attaching the gene (called the CAT gene) which codes for the CAT enzyme to it, and observing whether the CAT enzyme is produced. (05 Jan 1998) |