Amino acid is a compound in which the hydrogen atom on the carbonyl group of the carboxylic acid is substituted with an amino group, and the amino acid molecule contains both the amino group and the carboxyl group. Similar to the hydroxy acid, the amino acids can be divided into α-β-, γ -... w-amino acids according to the different positions of the amino groups on the carbon chain, but the amino acids obtained by the hydrolysis of the proteins are both α-amino acids There are only twenty species, they are the basic units that make up the protein.
Amino acids are the basic substances that make up the protein needed for animal nutrition. Is an organic compound containing a basic amino group and an acidic carboxyl group. The amino group is an α-amino acid attached to the α-carbon. Most of the amino acids that make up the protein are α-amino acids.
Amino acids in the human body through metabolism can play the following effects: ① synthetic tissue protein; ② into acid, hormones, antibodies, creatine and other ammonia substances; ③ into carbohydrates and fats; ④ oxidation of carbon dioxide and water and urea, generate energy
Amino acids for the colorless body, the melting point of more than 200 ℃, higher than the average melting point of organic compounds. α-amino acid acid, sweet, bitter, fresh 4 different taste. Glutamic acid monosodium salt and glycine is the largest amount of flavor seasoning. Amino pass is generally soluble in water, acid solution and alkaline solution, insoluble or slightly soluble in ethanol or ether and other organic solvents. The solubility of amino acids in water is very different. For example, the solubility of tyrosine is the smallest. At 25 ℃, tyrosine dissolves only 0.045 g in 100 g of water, but the solubility of tyrosine in hot water towel is large. Lysine and arginine often exist in the form of hydrochloride, because they are easily soluble in water, due to deliquescence and difficult to produce crystals .
(1) color and color A variety of common amino acids easily become colorless crystals, crystal shape due to the structure of amino acids vary. Such as L-glutamic acid for the four-column cylindrical crystal, D-glutamic acid was diamond-like crystal.
(2) melting point amino acid crystallization of the melting point is high, generally 200 ~ 300 ℃, many amino acids at or near the melting point will break down into amine and CO2.
(3) solubility Most of the amino acids can be dissolved in water. The solubility of different amino acids in water is different, such as lysine, arginine, proline solubility is greater, tyrosine, cysteine, histidine solubility is very small. A variety of amino acids can be dissolved in strong alkali and strong acid. But amino acids are insoluble or slightly soluble in ethanol.
(4) taste of amino acids and their derivatives have a certain sense of taste, such as acid, sweet, bitter, and so on. The taste of the species and the type of amino acids, three-dimensional structure. From the three-dimensional structure, in general, D-type amino acids are sweet, the sweetness of the higher than the corresponding L-type amino acids.
(5) UV absorption characteristics of a variety of common amino acids on the visible light are no absorption capacity. But tyrosine, tryptophan and phenylalanine in the ultraviolet region has obvious light absorption phenomenon. And most of the protein contains these three amino acids, especially tyrosine. Therefore, the protein content can be quantitatively detected using the UV absorption characteristic at a wavelength of 280 hm.
Preparation of amino acids
Most of the amino acids that make up the protein are biochemically synthesized by the Embden-Meyerhof pathway with the citric acid intermediate. The exception is the aromatic amino acid, histidine, the former biosynthesis with pentose phosphate pentose intermediate erythro-4-phosphate, which is synthesized by ATP with phosphoric acid ribose pyrophosphate. Microbes and plants can synthesize all the amino acids in the body, animals have a part of the amino acid can not be synthesized in vivo (essential amino acids). Essential amino acids are generally metabolized by carbohydrates, and more than 14 enzymes are required for biosynthesis, non-essential amino acid synthesis by multi-step reaction (6 steps or more), and the synthesis of essential amino acids requires more, About 60 kinds of enzymes involved. Biosynthetic amino acids, in addition to the synthesis of protein as raw materials, but also for alkaloids, lignin and other synthetic. On the other hand, the amino acid is decomposed in the living body due to the formation of keto acid by amino shift or oxidation, or is decomposed by decarboxylation to an amine