Biochemistry

In addition to the a-amino and a-carboxyl groups, in the total charge of the molecule in the composition of acidic and basic amino acids there is also a third - ionogenic group in the side chain. Such amino acids carry an additional negative or positive charge. The bipolarity of amino acid molecules determines their properties such as good solubility in water, high dielectric constants and melting points. too °c 0 A Z OH h 2 N-CH-COOH 2 X . + 2 1 A S OH R 0 Amino acid Ninhydrin О О О НО + CO 2 + RCHO + 3H 2 O Aldehyde Ruemann Purple The course of organic chemistry examines the chemical reactions characteristic of amino acids: salt formation (in NH 2 and COOH- groups), oxidation and reduction (in HS and S-S groups), alkylation, acylation and esterification (in NH 2 , OH- and COOH- groups), amidation (by COOH groups), nitration and halogenation (by aromatic nucleus), phosphorylation and sulfitation (by OH-groups), etc. Some of these reactions occur in living organisms. The functional groups of amino acids are diverse, which makes it possible to detect most of them using color reactions. Many of them, very sensitive and specific, reveal even small amounts of amino acids in complex mixtures, biological raw materials of plant and animal origin, and proteins. The ninhydrin reaction underlies the quantification of amino acids and proteins. Within the ninhydrin interacts with the a-amino group, a blue-violet product is formed with a maximum absorption at 580 nm; the color intensity is proportional to the amount of amino acid. The amino acid proline gives a yellow color with ninhydrin (maximum absorption at 440 nm). This reaction is used in various types of chromatography to identify and quantify amino acids. Amino groups of amino acids (peptides, proteins) can react with carbonyl groups of aldehydes and reducing sugars. These are melanoidinogenesis reactions. They can be schematically represented in two stages: 44