مصادر الكيمياء موقع لتعليم الكيمياء بصورة مبسطة

acid ceramidase , other name: N-acylsphingosine deacylase; a lysosomal enzyme that catalyses the hydrolyis of ceramide to sphingosine and a fatty acid. Its activity requires sphingolipid activator proteins (i.e. saposins B and C) and negatively charged phospholipids. A genetic locus at 8p21.3-22 encodes a precursor that contains 395 amino acids and is proteolytically cleaved into an a subunit (≈13 kDa) …

acetyl coenzyme A or acetyl-CoA; a derivative of coenzyme A in which the sulfhydryl group is acetylated. Originally termed ‘active acetate’, it is an important metabolite, derived from pathways such as glycolysis, fatty-acid oxidation, and degradative metabolism of some amino acids. It is further metabolized by the tricarboxylic- acid cycle and represents a key intermediate in lipid and terpenoid biosynthesis …

acetylcholinesterase ,systematic name: acetylcholine acetylhydrolase; other names: true cholinesterase; cholinesterase I; an esterase enzyme that catalyses the hydrolysis of acetylcholine to choline and acetate; it also acts on a variety of acetic esters and catalyses transacetylations. It is found in or attached to cellular or basement membranes of presynaptic cholinergic neurons and postsynaptic cholinoceptive cells. A soluble form occurs in …

A naturally occurring quaternary ammonium cation ester, with the formula CH3(O)COC2H4N(CH)3+, that plays a prominent role in nervous system function. The great importance of acetylcholine derives from its role as a neurotransmit­ter for cholinergic neurons, which innervate many tissues, including smooth muscle and skeletal muscle, the heart, ganglia, and glands. The effect of stimulating a cholinergic nerve, for example, the …

accessory pigment any of the, such as the yellow, red, or purple carotenoids and the red or blue phycobiliproteins in photosynthetic cells. The carotenoids are always present, whereas the phycobiliproteins occur only in algae belonging to the Rhodophyceae, the Cyanophyceae, and the Cryptophyceae. Strictly speaking, chlorophyll b is also an accessory pigment.

acetogenin any substance built up of two-carbon units that may formally be considered to derive from a polyacetyl chain intermediate; the carbon atoms derived from the carboxyl carbon atoms of acetic acid frequently remain oxidized. It is not a recommended term.

acetazolamide an inhibitor of carbonic anhydrase that is useful as a diuretic. It acts by preventing bicarbonate reabsorption in the proximal tubules of the kidney.

acetate–CoA ligase EC 6.2.1.1; systematic name: acetate:CoA ligase (AMP-forming); other names: acetyl–CoA synthetase; acyl-activating enzyme; acetate thiokinase; acetyl-activating enzyme. An enzyme that catalyses a reaction between ATP, acetate, and CoA to form AMP, pyrophosphate, and acetyl-CoA. It is an important enzyme in organisms (e.g. Escherichia coli, many fungi, protozoans, algae) that utilize acetate as a carbon source. Distinguish from acetate– …

acesulfame 6-methyl-1,2,3-oxathiazin-4(3H)-one 2,2′-dioxide; a sweet-tasting material that, as the potassium salt, has been used in foods and cosmetics.

Aces abbreviation for N-(2-acetamido)-2-aminoethane sulfonic acid; 2-[(2-amino-2-oxoethyl)amino]ethane sulfonic acid; a Good buffer substance, pKa (20°C) = 6.9.