Catalytic activity:L-tyrosine + tetrahydrobiopterin + O (2) = 3 ,4-dihydroxy-L-phenylalanine + 4a-hydroxytetrahydrobiopterin. ,cofactor:Fe (2+) ion. ,Disease:Defects in TH are the cause of dystonia DOPA-responsive autosomal recessive (ARDRD) [MIM:605407]; also known as autosomal recessive Segawa syndrome. ARDRD is a form of DOPA-responsive dystonia presenting in infancy or early childhood. Dystonia is defined by the presence of sustained involuntary muscle contractions , often leading to abnormal postures. Some cases of ARDRD present with parkinsonian symptoms in infancy. Unlike all other forms of dystonia , it is an eminently treatable condition , due to a favorable response to L-DOPA. ,enzyme regulation:Phosphorylation leads to an increase in the catalytic activity. ,Function:Plays an important role in the physiology of adrenergic neurons. ,online information:Tyrosine hydroxylase entry ,pathway:Catecholamine biosynthesis; dopamine biosynthesis; dopamine from L-tyrosine: step 1/2. ,similarity:Belongs to the biopterin-dependent aromatic amino acid hydroxylase family. ,tissue specificity:Mainly expressed in the brain and adrenal glands. ,
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