| gap junction | <cell biology> A junction between two cells consisting of many pores that allow the passage of molecules up to about 900D. Each pore is formed by an hexagonal array (connexon) of six transmembrane proteins (connexins) in each plasma membrane: when mated together the pores open, allowing communication and the interchange of metabolites between cells. Electrical synapses are gap junctions and metabolic cooperation depends upon the formation of gap junctions. (18 Nov 1997) |
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| androst-5-ene-3 beta,17 beta-diol | <chemical> An adrenal-derived oestrogenic metabolite of dhea. Evidence exist for its use as an endocrine regulator of immune response. Pharmacological action: anabolic steroids. Chemical name: Androst-5-ene-3,17-diol, (3beta,17beta)- (12 Dec 1998) |
| beta-1,3-galactosyl-0-glycosyl-glycoprotein beta-1,3-N-acetylglucosaminyltransferase | <enzyme> Capable of adding a glcnac residue to g1cnacman(3)g1cnac; from mung bean seedlings Registry number: EC 2.4.1.146 Synonym: n-acetylglucosaminyltransferase II, gal3-(glcnac6)galnac-mucin (glcnac--gal)3-glcnactransferase (26 Jun 1999) |
| beta-1,3-galactosyl-O-glycosyl-glycoprotein beta-1,6-acetylglucosaminyl transferase | <enzyme> With EC 2.4.1.148 this is called beta6-glcnac-transferase b Registry number: EC 2.4.1.102 Synonym: gal3-galnac-mucin-6-glcnac transferase, udp-glcnac-gal1-3galnac-r-(glcnac to galnac)-beta1-6glcnac transferase, core 2 glcnac transferase, core 2-n-acetylglucosaminyltransferase, core 2 beta6-gn-t (26 Jun 1999) |
| beta-1,4-mannosyl-glycoprotein beta-1,4-N-acetylglucosaminyltransferase | <enzyme> Induced in preneoplastic stage of liver carcinogenesis promoted by orotic acid in rats; adds "bisecting n-acetylglucosaminyl residue in beta 1,4 linkage to the beta-linked mannose of the core of asparagine-linked oligosaccharides Registry number: EC 2.4.1.144 Synonym: n-acetylglucosaminyltransferase III, udpgnac-glycopeptide beta4-n-acetylglucosaminyl transferase III, udpgnac-magtransferase III, udp-n-acetylglucosamine-beta-d-mannoside beta-1,4-n-acetylglucosaminyltransferase III (26 Jun 1999) |
| beta-hydroxy-beta-methylglutaryl-CoA | -OOCCH2C(OH)(CH3)CH2COS-CoA;a key intermediate in the synthesis of ketone bodies and of steroids. Synonym: 3-hydroxy-3-methylglutaryl-CoA. Beta-hydroxy-beta-methylglutaryl-lyase, an enzyme, found primarily in liver and rumen epithelium that catalyses the formation of acetyl-CoA and acetoacetate from beta-hydroxy-beta-methylglutaryl-CoA; a key step in ketogenesis; a deficiency of this enzyme leads to episodes of severe metabolic acidosis without ketosis. Beta-hydroxy-beta-methylglutaryl-reductase, an enzyme that catalyses the rate-limiting step of cholesterol biosynthesis, beta-hydroxy-beta-methylglutaryl-CoA + 2NADPH + 2H+ → mevalonate + 2NADP+ + coenzyme A. Beta-hydroxy-beta-methylglutaryl-synthase, an enzyme in mitochondria that catalyses the reaction of acetyl-CoA with acetoacetyl-CoA and water to form beta-hydroxy-beta-methylglutaryl-CoA and coenzyme A, a step required for both ketogenesis and steroidogenesis to occur. (05 Mar 2000) |
| beta-n-acetylglucosaminylglycopeptide beta-1,4-galactosyltransferase | <enzyme> An enzyme that catalyses the transfer of galactose from udp-galactose to a specific glycoprotein receptor, 2-acetamido-2-deoxy-d-glucosyl-glycopeptide, during glycopeptide synthesis. Chemical name: UDPgalactose:N-acetyl-beta-D-glucosaminylglycopeptide beta-1,4-galactosyltransferase Registry number: EC 2.4.1.38 (12 Dec 1998) |
| beta, or beta-value | <radiobiology> Ratio of plasma kinetic pressure to magnetic-field pressure, proportional to the ratio of plasma kinetic energy density to magnetic field energy density. Beta is usually measured relative to the total, local field (loosely called beta toroidal), but sometimes the plasma pressure relative to only the poloidal component of the field (beta poloidal) or relative to some external field (like the maximum field at the magnetic coils) is more useful. There is also a normalised beta (beta_N) of interest when discussing the beta limit. (lots of help from Art Carlson with the above.) Because the cost of a reactor is strongly influenced by the strength of the magnetic field that must be provided, beta values are directly related to the economics of fusion power production. Beta is usually expressed as a percentage, with 5% generally believed to be the minimum value required for an economical fusion reactor. See: pressure, kinetic pressure, magnetic pressure, second stability. (09 Oct 1997) |
| UDP-GalNAc-beta-galactose beta 1,4-N-acetylgalactosaminyltransferase | <enzyme> Consider also EC 2.4.1.92 Registry number: EC 2.4.1.- Synonym: beta-1,4-n-acetylgalactosaminyltransferase, 4-galnactransferase, udp-n-acetylgalactosamine-beta-galactose beta 1,4-n-acetylgalactosaminyltransferase, (1-4)-n-acetyl-beta-d-galactosaminyltransferase, galnact-1 (26 Jun 1999) |
| 5 alpha-androstane-3 beta,17 beta-diol 6 alpha-hydroxylase | <enzyme> Requires NADPH, found in rat prostatic microsomes Registry number: EC 1.14.13.- Synonym: artdl 6 alpha-hydroxylase (26 Jun 1999) |
| 5 alpha-androstane 3 beta,17 beta-diol 7 alpha-hydroxylase | <enzyme> Requires NADPH, found in rat prostate microsomes Registry number: EC 1.14.13.- Synonym: artdl 7 alpha-hydroxylase (26 Jun 1999) |
| air-bone gap | The difference between the threshold for hearing acuity by bone conduction and by air conduction. (05 Mar 2000) |
| air-gap radiography | Chest radiography with a space (at least 10 inches) between the subject and film. Instead of using a grid, this method uses the geometry and X-ray absorption by the air to remove scattered radiation. (05 Mar 2000) |
| air-gap technique | Chest radiography performed using a space between the subject and film instead of a grid to absorb scattered radiation; usually requires a target-film distance of 10 feet. (05 Mar 2000) |
| anion gap | <biochemistry> The difference between the sum of the measured cations and anions in the plasma or serum calculated as follows: (Na + K) -(Cl + HCO3) = < 20 mmol/l. Elevated values may occur in diabetic or lactic acidosis; normal or low values occur in bicarbonate-losing metabolic acidoses. Synonym: cation-anion difference. (05 Mar 2000) |