Tyrosine aminotransferase

Tyrosine Aminotransferase (TAT) is an enzyme that plays a crucial role in the metabolism of amino acids, specifically in the catabolic pathway of tyrosine - an important amino acid involved in various physiological processes. TAT catalyzes the transfer of an amino group from tyrosine to alpha-ketoglutarate, producing p-hydroxyphenylpyruvate and glutamate. This reaction is a key step in the conversion of tyrosine into fumarate and acetoacetate, which can then enter the Krebs cycle for energy production or be used in the synthesis of other molecules.

Function

The primary function of tyrosine aminotransferase is to facilitate the degradation of tyrosine, which is necessary for maintaining its proper levels within the body and for the production of energy. Tyrosine is not only a building block for protein synthesis but also a precursor for several significant biochemical compounds, including thyroid hormones, melanin, and dopamine. By regulating tyrosine levels, TAT indirectly influences various physiological functions, such as pigment formation, mood regulation, and metabolic rate.

Genetics

The gene responsible for encoding tyrosine aminotransferase is located on chromosome 16 (16q22.1-22.3) in humans. Mutations in this gene can lead to a rare metabolic disorder known as Tyrosinemia type II (or Richner-Hanhart syndrome), characterized by elevated blood levels of tyrosine, leading to eye, skin, and intellectual disabilities.

Clinical Significance

1. 1. 1. Tyrosinemia Type II

This autosomal recessive disorder results from deficient activity of tyrosine aminotransferase. Symptoms often appear in early childhood and include painful lesions on the palms and soles, corneal ulcers, and developmental delays. Dietary restriction of phenylalanine and tyrosine is the mainstay of treatment, along with supportive care for symptoms.

1. 1. 1. Diagnostic and Therapeutic Applications

Measurement of TAT activity in the liver can be used for the diagnosis of Tyrosinemia type II. Moreover, understanding the regulation and function of TAT has potential implications in developing therapies for disorders related to tyrosine metabolism, including certain types of cancer where tyrosine kinase enzymes are overactive.

Regulation

The activity of tyrosine aminotransferase is subject to complex regulatory mechanisms, including hormonal control by glucocorticoids and feedback inhibition by its substrates. This ensures that tyrosine levels are finely tuned according to the body's metabolic needs.

See Also

• Amino acid metabolism
• Liver function tests
• Metabolic disorder