- 2-Amino-3-(4-hydroxyphenyl)propionic acid; 3-(4-hydroxyphenyl)alanine; the l-isomer is an α-amino acid present in most proteins.- t. aminotransferase an enzyme that catalyzes the reversible reaction of l-t. and α-ketoglutarate producing p-hydroxyphenylpyruvate and l-glutamate; this enzyme catalyzes a step in l-phenylalanine and l-t. catabolism; a deficiency of this enzyme is associated with tyrosinemia II. SYN: t. transaminase.- t. iodinase a postulated enzyme in the thyroid catalyzing iodination of t., a reaction important in the eventual biosynthesis of thyroxine. SEE ALSO: peroxidases.- t. kinase an enzyme that phosphorylates tyrosyl residues on certain proteins; many are products of viral oncogenes; a number of receptors ( e.g., receptors for epidermal growth factor, insulin, etc.) have this enzymatic activity; a misnomer, since the physiologic substrate is not t. but tyrosyl residues in a protein.- t. phenol-lyase an enzyme catalyzing the hydrolysis of l-t. to phenol, pyruvate, and NH3. SYN: β-tyrosinase.- t. transaminase SYN: t. aminotransferase.
* * *ty·ro·sine 'tī-rə-.sēn n a phenolic amino acid C9H11NO3 that is a precursor of several important substances (as epinephrine and melanin) abbr. Tyr
* * *n.
* * *ty·ro·sine (Tyr) (Y) (tiґro-sēn) a nonessential amino acid, β-p-hydroxyphenylalanine, found in most proteins and synthesized metabolically from phenylalanine; it is a precursor of thyroid hormones, catecholamines, and melanin. See also table at amino acid. [USP] a preparation of tyrosine used as a dietary supplement.
Medical dictionary. 2011.