Phosphorylation Sites on Tyrosine Hydroxylase
Tyrosine Hydroxylase (TH), the rate limiting enzyme in the biosynthesis of the catecholamine neurotransmitters, is regulated by protein phosphorylation. Previously, it has been demonstrated that tyrosine hydroxylase is phosphorylated by cyclic AMP-dependent protein kinase (PK A)(1–4) and calmodulin-dependent protein kinase (Cam K) (5–6). Recently, calcium and phospholipid-dependent protein kinase (PK C) has been reported to phosphorylate tyrosine hydroxylase (7,8). More recently, Roskoski et al. (9) have demonstrated that tyrosine hydroxylase is also a substrate of cyclic GMP dependent protein kinase (PK G). This communication compares the sites in tyrosine hydroxylase that are phosphorylated by each of these kinases. An endogenous kinase has been found to be present in the preparation of the purified tyrosine hydroxylase. Using the sequence of tyrosine hydroxylase derived from the cDNA and the sequences of the phosphopeptides produced from tryptic digestion of the phosphorylated enzyme, the specific sites of phosphorylation can be identified.
KeywordsTyrosine Hydroxylase Phosphorylation Site Chromaffin Cell Tryptic Digestion Catecholamine Biosynthesis
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