THREONINE

From Big Medical Encyclopedia

TREONYN (Tre) — and - ampno-r-ok-simaslyanaya acid, one of the most important irreplaceable amino acids which are a part of proteins of plant and animal origin.

T. it is eurysynusic in the nature. Are richest with it such it is white - to as pepsin (see), gliadine (see), fibrin (see)*. In the majority of natural proteins the maintenance of T. makes 2 — 6%. Contains in a blood plasma of the person 1 — 3 laid down / 100 ml free T., in daily amount of urine of the healthy person — 28 mg. At pregnancy note a nek-swarm increase in allocation of T. with urine.

T. it was open and allocated in 1935 during the studying of hydrolyzates of fibroin (see). T. represents white crystal matter, well water soluble. In alkaline condition of T. it is unstable and collapses with formation of glycine (see) and and - aminobutyric to - you (see. Aminobutyric acids).

T. is monoamino monocarboxylic to - that (see Amino acids) and like all amino acids received from natural proteins has and - an amino group (a-NIT2-rpyn-pu) attached to the carbon atom connected with SOON-group; — the group replacing one of hydrogen atoms at | 3-carbon atom — enter into the list of the side radical of a molecule of threonine methyl (SN3-) and oksi-(IT-) groups:

Oxygroup T. the T has very weak acid properties, thanks to it. it is capable to formation of ethers phosphoric and organic acids. It serves also as the place of accession of sugar rings to the rest of T. in molecules of glycoproteins (see).

As well as all amino acids (except for glycine), T. exists in two L-and D-stereopzomernykh (enantiomeric) forms (see the Isomerism). Only the L-configuration is biologically active. Molecule T., in turn, can have various dimensional orientation of groups around the second asymmetric carbon atom. These optical antipodes carry the names L-and D-allotreoninov; L-threonine is received hydrolysis of natural proteins. There are ways of chemical synthesis of T. from acetic aldehyde (see Aldehydes) and glycine.

Methods of determination of T. are based on quantitative definition of the acetic aldehyde which is formed at oxidation of threonine some specific reagents (see Acetaldehyde).

Ability to synthesize these or those amino acids is very not identical at various organisms. The higher plants, many bacteria and mushrooms are capable to produce all amino acids necessary for them for synthesis of protein, using ammonia and nitrates as a source of nitrogen. A predecessor of L-threonine at its biosynthesis at these organisms is aspartic acid (see). This multistage process is regulated by the principle of a feed-back: surplus of T. inhibits the enzyme responsible for the first reaction of a biosynthetic way. Actually T. it is formed of homoserine, fosforili-rovanny at the expense of ATP (see Serine) during the final reaction catalyzed by enzyme threoninesynthase (KF 4. 2. 99. 2). In an organism of the highest animals and the person a number of the previous reactions is not carried out. For this reason of T. carry to number of so-called irreplaceable amino acids, to-rye the person and the highest animals shall receive with food.

Daily need of the adult for T. makes 0,5 — 1 g; newborns have a need for T. several times above. In T, full-fledged on contents. meat and meat products and fish are, T are especially rich. eggs and milk. Products of plant origin contain T. in smaller quantities.

In a human body there are several ways of a catabolism of T. On one of them it is exposed to dehydration and deamination with the participation of enzyme of a treonindegid-rataza (KF 4. 2. 1. 16), therefore it is formed and - oxobutyric to - that. In animal fabrics there is enzimatic degradation of T. on glycine and acetic aldehyde with the participation of piridoksalfosfatzavisi-my enzyme of threoninezymohexase (KF 2. 1. 2. 1).

Bibliography: Berezov T. T. and K O'

rovkiv B. F. Biological chemistry, M., 1982; Lenindzher A. Biochemistry, the lane with English, M., 1976; M e and l of e r D. Biokhimiya, the lane with English, t. 1 — 3, M., 1980; Whyte A., etc. Fundamentals of biochemistry, a per, with English, t „1 — 3, M., 1981.

II. JI. Ivanov.

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