L-threonine Import Concessions,Metabolism and Conversion

The metabolic pathways and biotransformations of L-threonine are complex yet orderly processes, and the specific introduction is as follows:

I. Metabolic Pathways

Threonine Dehydratase Pathway: In most microorganisms and animals, L-threonine first undergoes a dehydration reaction under the action of threonine dehydratase to produce α-ketobutyric acid. This substance can be further decarboxylated to produce propionyl-CoA under the action of the α-ketoglutarate dehydrogenase complex. Then, through a series of reactions, it finally generates succinyl-CoA, which enters the tricarboxylic acid cycle (TCA cycle) and participates in energy metabolism.

Threonine Dehydrogenase Pathway: In some microorganisms, there exists threonine dehydrogenase. Under its action, L-threonine first undergoes a dehydrogenation reaction to produce 2-amino-3-oxobutyric acid, and then through a deamination reaction, it generates pyruvate and glycine. Among them, pyruvate can enter the glycolysis or gluconeogenesis pathway, while glycine can participate in various biosynthetic processes, such as the synthesis of purines, pyrimidines, porphyrins, etc.

Threonine Aldolase Pathway: In tissues such as the liver, L-threonine can be cleaved into glycine and acetaldehyde under the catalysis of threonine aldolase. Glycine can participate in various biosynthetic processes as mentioned above, and acetaldehyde can be converted into acetic acid under the action of acetaldehyde dehydrogenase, and further generate acetyl-CoA, which enters the TCA cycle or participates in metabolic processes such as fatty acid synthesis.

II. Biotransformations

Microbial Transformation: Many microorganisms have the ability to convert L-threonine into other useful substances. For example, certain strains of Corynebacterium glutamicum can use L-threonine as a raw material to synthesize L-isoleucine through specific metabolic pathways. In this process, L-threonine first undergoes the action of a series of enzymes such as threonine dehydratase to generate intermediate products, and then through the catalysis of other enzymes, it finally synthesizes L-isoleucine. In addition, some microorganisms can also convert L-threonine into bioactive substances. For instance, certain actinomycetes can convert it into polypeptide substances with antibacterial activity.

Plant Transformation: In plants, L-threonine also participates in various biotransformation processes. For example, in the nitrogen metabolism and amino acid metabolism network of plants, it can serve as a carrier of nitrogen and carbon sources and participate in the synthesis of various secondary metabolites such as proteins, alkaloids, and flavonoids. In the defense responses of some plants, L-threonine may be converted into substances with antibacterial and insecticidal activities to resist the invasion of external pathogens and pests.

Transformation in Animals: In addition to the above metabolic pathways, L-threonine can also participate in some special biotransformation processes in animals. For example, in the liver and kidneys of mammals, part of L-threonine can be converted into taurine. This process requires the participation of multiple enzymes.

L-threonine generates cysteine under the action of relevant enzymes, and then cysteine undergoes a series of reactions such as oxidation and decarboxylation to finally produce taurine. Taurine has many important physiological functions in animals, such as regulating cell osmotic pressure, participating in the metabolism of bile acids, and having antioxidant effects, etc.