| beta-ketoacyl-ACP synthase | <enzyme> An enzyme condensing malonyl-ACP and acyl-cys-protein to 3-oxoacyl-ACP + cys-protein + CO2, and similar reactions, as steps in fatty acid synthesis; cys-protein is also a part of the fatty acid synthase complex. Synonym: acyl-malonyl-ACP synthase, beta-ketoacyl-ACP synthase. (05 Mar 2000) |
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| beta-ketoadipyl-coenzyme A thiolase | <enzyme> Last enzyme in the beta-ketoadipate pathway in pseudomonas putida; genbank l33795 Registry number: EC 2.3.1.- Synonym: pcaf gene product, beta-ketoadipyl-CoA thiolase (26 Jun 1999) |
| beta-ketohydrogenase | Beta-Hydroxyacyl dehydrogenase;enzyme catalyzing the oxidation of an l-3-hydroxyacyl-CoA to a 3-ketoacyl-CoA with reduction of NAD+; one of the enzymes of the b oxidation of fatty acids. Synonym: beta-ketohydrogenase, beta-ketoreductase. (05 Mar 2000) |
| beta-ketoreductase | Beta-Hydroxyacyl dehydrogenase;enzyme catalyzing the oxidation of an l-3-hydroxyacyl-CoA to a 3-ketoacyl-CoA with reduction of NAD+; one of the enzymes of the b oxidation of fatty acids. Synonym: beta-ketohydrogenase, beta-ketoreductase. (05 Mar 2000) |
| beta-ketothiolase | <enzyme> An enzyme catalyzing the thioclastic cleavage by coenzyme A of beta-ketoacyl-CoA, forming an acyl-CoA with a carbon chain shorter by two atoms, the missing two atoms appearing as acetyl-CoA. A step in fatty acid degradation. See: acetyl-CoA acetyltransferase. Synonym: 3-ketoacyl-CoA thiolase, beta-ketothiolase. (05 Mar 2000) |
| beta-lactamase | <enzyme> An enzyme produced by some bacteria, which causes the breakdown of the active form of some penicillin antibiotics, rendering them ineffective. It causes the hydrolysis of a beta-lactam (as penicillin to penicilloic acid); found in most strains of staphylococcus bacteria that are naturally resistant to penicillin. Synonym: cephalosporinase, penicillinase. (05 Mar 2000) |
| beta-lactamase inhibitor | <pharmacology> Drugs such as clavulanic acid, which are used to inhibit bacterial beta-lactamases; often used with a penicillin or cephalosporin to overcome drug resistance. (05 Mar 2000) |
| beta-lactamases | <enzyme> Enzymes found in many bacteria which catalyze the hydrolysis of the amide bond in the beta-lactam ring. Well known antibiotics destroyed by these enzymes are penicillins and cephalosporins. Chemical name: beta-Lactamhydrolase Registry number: EC 3.5.2.6 (12 Dec 1998) |
| beta limit | <radiobiology> if the plasma pressure in a tokamak becomes too high, the so-called ballooning modes become unstable and lead to a loss of confinement (sometimes catastrophic, sometimes not). The exact value at which this occurs depends strongly on the magnetic field B, the plasma minor radius a, and the toroidal plasma current I, such that maximum value of the normalised beta, beta_N=betaBa/I, is around 4% (with B in Teslas, a in metres, and I in Mega-amperes). The exact value depends on details of the plasma shape, the plasma profiles, and the safety factor. Synonym: troyon limit. (09 Oct 1997) |
| beta-mercaptoethanol | HO-CH2-CH2-SH;a reagent used to reduce disulfide bonds, particularly in proteins, and to prevent their formation. Synonym: beta-mercaptoethanol. (05 Mar 2000) |
| beta-n-acetylhexosaminidase | <enzyme> An enzyme hydrolyzing terminal non-reducing n-acetyl-d-hexosamine residues in n-acetyl-beta-d-hexosaminides. It acts on glucosides, galactosides, and several oligosaccharides. Hexosaminidase a cleaves gm2, ga2, globosides, and hexosamine oligosaccharides. Deficiency of this isoenzyme causes tay-sachs disease. Hexosaminidase b cleaves all the above substrates except gm2. A deficiency of both a and b causes sandhoff disease. The enzyme has also been used as a tumour marker to distinguish between malignant and benign disease. Chemical name: beta-N-Acetyl-D-hexosaminide N-acetylhexosaminohydrolase Registry number: EC 3.2.1.52 (12 Dec 1998) |
| beta-naphthoflavone | <chemical> A polyaromatic hydrocarbon inducer of p4501a1 and p4501a2 cytochromes. (proc soc exp biol med 1994 dec:207(3):302-308) Pharmacological action: enzyme inhibitors. (12 Dec 1998) |
| beta-normal | <radiobiology> Beta-N, the normalised beta, is beta relative to the beta limit. (09 Oct 1997) |
| beta-oxidation | <biochemistry> The oxidative breakdown of fatty acids into acetyl-coenzyme A by repeated oxidation at the beta-carbon atom. Oxidation of the beta-carbon (carbon 3) of a fatty acid causes the formation of the beta-keto (beta-oxo) acid analog. This is of importance in fatty acid catabolism, the entire pathway for the catabolism of saturated fatty acids containing an even number of carbon atoms. Beta-oxidation is a part of this pathway and acetyl-CoA is a major product of this pathway. (05 Mar 2000) |
| beta-oxidation-condensation theory | <biochemistry> That the two carbon fragments split from the fatty acid molecule by beta-oxidation are converted to acetic acid and then condensed to acetoacetic acid. (05 Mar 2000) |