| sigma factor | Initiation factor (86 kD) that binds to E. Coli DNA dependent RNA polymerase and promotes attachment to specific initiation sites on DNA. Following attachment, the sigma factor is released. (18 Nov 1997) |
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| receptors, sigma | A class of cell surface receptors recognised by its pharmacological profile. Sigma receptors were originally considered to be opioid receptors because they bind certain synthetic opioids. However they also interact with a variety of other psychoactive drugs, and their endogenous ligand is not known (although they can react to certain endogenous steroids). Sigma receptors are found in the immune, endocrine, and nervous systems, and in some peripheral tissues. (12 Dec 1998) |
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| sigma | The 18th letter of the Greek alphabet, σ. (05 Mar 2000) |
| sigma bond | <chemistry> A bond formed from the overlap of either two s-orbitals or two hybrid orbitals such as sp3 or sp2 orbitals. (09 Jan 1998) |
| sigma effect | The decrease in apparent viscosity that occurs when a suspension, such as blood, is made to flow through a tube of smaller diameter; observed in tubes less than about 0.3 mm in diameter. Synonym: sigma effect. (05 Mar 2000) |
| sigma peptide | A peptide with one end bonded to a point within the chain, usually by means of the disulfide group of a cystine residue, so that only one end of the peptide is free; so called since the peptide chain has then the rough shape of the Greek letter sigma; e.g., oxytocin. (05 Mar 2000) |
| accelerator factor | <chemical> Heat- and storage-labile plasma glycoprotein which accelerates the conversion of prothrombin to thrombin in blood coagulation. Factor v accomplishes this by forming a complex with factor xa, phospholipid, and calcium (prothrombinase complex). Deficiency of factor v leads to owren's disease. Chemical name: Blood-coagulation factor V (12 Dec 1998) |
| acetate replacement factor | <biochemistry> 1,2 dithiolane 3 valeric acid. Regarded as a coenzyme in the oxoglutarate dehydrogenase complex of the citric acid cycle. Involved generally in oxidative decarboxylations of _ keto acids. A growth factor for some organisms. (18 Nov 1997) |
| adrenal weight factor | A postulated substance of adenohypophysial origin responsible for maintenance of the weight of the adrenal cortex. (05 Mar 2000) |
| adrenocorticotropic releasing factor | Hormone produced by hypothalamus that causes pituitary to secrete adrenocorticotropic hormone. (05 Mar 2000) |
| a-factor | <molecular biology> A protein which is found in the bacterial genus Streptomyces that helps start the production of streptomycin and the process of morphological differentiation. It is used in biotechnology to induce these functions in mutant strains of Streptomyces that cannot produce it themselves. (09 Feb 1998) |
| angiogenesis factor | Substance causing proliferation of new blood vessels. It is found in tissues with high metabolic requirements, such as the retina, and in certain cancers. The factor is also released by hypoxic macrophages at the edges or outer surfaces of wounds and initiates revascularization in wound healing. (12 Dec 1998) |
| animal protein factor | <biochemistry> Member of the water soluble B vitamin group, important in the proper function of the nervous system and important in proper carbohydrate, protein and fat metabolism. (27 Sep 1997) |
| antialopecia factor | A member of the vitamin B complex necessary for growth of yeast and of mice, absence from the diet causes hair loss and dermatitis in mice. (27 Sep 1997) |
| antianaemic factor | <biochemistry> Member of the water soluble B vitamin group, important in the proper function of the nervous system and important in proper carbohydrate, protein and fat metabolism. (27 Sep 1997) |
| antiberiberi factor | Synonym: thiamin. (05 Mar 2000) |