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Effect of Cyclic AMP‐Dependent Protein Phosphorylating Conditions on the pH‐Dependent Activity of Tyrosine Hydroxylase from Beef and Rat Striata
Author(s) -
Pollock Robert J.,
Kapatos Gregory,
Kaufman Seymour
Publication year - 1981
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.1471-4159.1981.tb04471.x
Subject(s) - tyrosine hydroxylase , phosphorylation , pterin , chemistry , enzyme , tyrosine 3 monooxygenase , sephadex , cofactor , biochemistry , tyrosine , enzyme assay , tetrahydrobiopterin , dopamine , biology , endocrinology
Abstract Tyrosine hydroxylase (TH, EC 1.14.16.2) from beef brain striata was purified 23‐fold from an extract of an acetone powder. If this enzyme preparation is treated with a cyclic AMP‐dependent protein phosphorylation system, there is a change in the pH dependence of the enzyme activity. The pH optimum at saturating tetrahydrobiopterin (BH 4 ) concentration is shifted from below pH 6 to about pH 6.7. At pH 7, activation is expressed mainly as an increase in V max , whereas at pH 6, activation is expressed mainly as a decrease in K m for the pterin cofactor. Further, even with the control enzyme the K m for pterin cofactor declines precipitously as the pH is increased from 6 toward neutrality. Similar data were obtained with G‐25 Sephadex‐treated rat striatal TH. Experiments in which rat striatal synaptosomes were used demonstrated that the in situ activation of TH by phosphorylating conditions is expressed primarily as an increase in the maximum rate of dopamine synthesis. These results indicate that changes in TH activity caused by cyclic AMP‐dependent protein phosphorylation will depend to a large extent on the pH of the TH environment.