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Tyrosine Hydroxylase in “Leaky” Adrenal Medullary Cells: Evidence for In Situ Phosphorylation by Separate Ca 2+ and Cyclic AMP‐Dependent Systems
Author(s) -
Niggli V.,
Knight D. E.,
Baker P. F.,
Vigny A.,
Henry J.P.
Publication year - 1984
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1984.tb12784.x
Subject(s) - tyrosine hydroxylase , phosphorylation , tyrosine 3 monooxygenase , tyrosine , tyrosine phosphorylation , enzyme , adrenal medulla , catecholamine , chemistry , biology , biochemistry , endocrinology , medicine
The systems responsible for phosphorylating tyrosine hydroxylase, the rate‐limiting enzyme of catecholamine biosynthesis, were investigated in situ in adrenal medullary cells made permeable to solutes of up to 1,000 dalton by exposure to brief intense electric fields. Two different phosphorylation systems were found. One is dependent on Ca 2+ , the other on cyclic AMP. The Ca 2+ ‐dependent system is half‐maximally activated by 1‐2 μ M Ca 2+ and 0.5 m M ATP, and follows a time course similar to that of secretion of catecholamines. Trifluoperazine (0.1 m M ) does not inhibit significantly Ca 2+ ‐dependent phosphorylation of tyrosine hydroxylase in situ. The cyclic AMP‐dependent system is half‐maximally activated by addition of 0.5 μ M cyclic AMP and about 0.3 m M ATP. Ca 2+ ‐dependent and cyclic AMP‐dependent phosphorylations of tyrosine hydroxylase have roughly the same time course and are additive under conditions where one system is already saturated. Peptide maps of immunoprecipitated tyrosine hydroxylase, after in situ phosphorylation of the enzyme either in the presence of 10 −8 M Ca 2+ plus 2 × 10 −5 M cyclic AMP or of 10 −5 M Ca 2+ , show a marked difference indicating that the enzyme contains several phosphorylation sites. At least one of these sites is phosphorylated only by the Ca 2+ ‐dependent system, whereas the other site(s) are phosphorylated by both the Ca 2+ ‐ and cyclic AMP‐dependent systems. The effect of in situ phosphorylation of tyrosine hydroxylase on its enzymatic activity was also investigated.