Threonine

threonine (thrē`ənēn), organic compound, one of the 22 α-amino acids commonly found in animal proteins. Only the l-stereoisomer appears in mammalian protein. It is one of several essential amino acids needed in the diet; human beings cannot synthesize it from simpler metabolites. Young adults need about 14 mg of this amino acid per day per kilogram (6 mg per lb) of body weight. Although threonine participates in many reactions in bacteria, including the biosynthesis of vitamin B₁₂ and isoleucine, its metabolic role in higher animals, including man, remains obscure. It is known only as a constituent of proteins, and even in that form it is relatively unreactive. In spite of the fact that its side chain has a hydroxyl group similar to that of serine, there is no indication that it participates in the catalytic functions of any enzyme. Threonine was isolated from the protein fibrin in 1935 and synthesized in the same year.

---

threonine

One of the essential amino acids. It occurs in the proteins of egg, milk, gelatin, and other biological substances and may be synthesized or obtained by hydrolyzing casein. It is used in nutritional and biochemical research and as a dietary supplement.

---

threonine [′thrē·ə‚nēn]

(biochemistry)

CH₃CHOHCH(NH₂)COOH A crystalline α-amino acid considered essential for normal growth of animals; it is biosynthesized from aspartic acid and is a precursor of isoleucine in microorganisms.

---

Threonine 

α-amino-β-hydroxybutyric acid, a natural amino acid, CH₃CH(OH)CH(NH₂)COOH. It exists in four optically active forms and two racemates (L-, D-, and DL-threonine and L-, D-, and DL-allothreonine). Natural L-threonine was isolated in 1935 from acid hydrolysates of fibrin. L-threonine constitutes 2–6 percent of all natural proteins, except protamines.

Threonine is an essential amino acid. The daily requirement for adults is 0.5 g, and for children up to the age of 7, about 3 g. The precursor of L-threonine during biosynthesis in plants and microorganisms is aspartic acid. This multistage enzymic process is regulated according to the feedback principle: excess threonine inhibits the first enzyme on the path to the biosynthesis of threonine. There are various possible pathways for the decomposition of threonine in the body; they lead to the formation of a-ketobutyric acid, acetaldehyde, and glycine, as well as pyruvic acid.

A method for the chemical synthesis of L-threonine from acetaldehyde and glycine has been developed.

REFERENCE

Meister, A. Biokhimiia aminokislot. Moscow, 1961. (Translated from English.)

E. N. SAFONOVA