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SYNAPTOSOMAL TYROSINE HYDROXYLATION: AFFINITY FOR OXYGEN
Author(s) -
Davis J. N.
Publication year - 1977
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.1471-4159.1977.tb10667.x
Subject(s) - tyrosine , hydroxylation , incubation , oxygen , chemistry , biochemistry , synaptosome , catecholamine , substrate (aquarium) , tyrosine hydroxylase , enzyme , biology , in vitro , endocrinology , organic chemistry , ecology
— Crude striatal synaptosomes were used to determine the affinity of brain tyrosine 3‐mono oxygenase for oxygen. The rate of tyrosine hydroxylation was determined at several different oxygen concentrations using L‐[ 14 C]tyrosine as substrate and measuring the [ 14 C]DOPA formed in the presence of a decarboxylase inhibitor. The accumulation of [ 14 C]tyrosine by synaptosomes was unaffected by incubation in nitrogen or 2.3% oxygen. Preincubation in nitrogen for up to 4 h did not impair the ability of synaptosomes to hydroxylate tyrosine when returned to air. Furthermore, pre‐incubation in either nitrogen or air produced similar changes in the ultrastructural appearance of the synaptosomes and mitochondria in the crude preparation used in these studies. Thus tyrosine hydroxylation in these synaptosomes appeared to reflect tyrosine 3‐mono oxygenase activity over a range of oxygen concentrations. The apparent K m for oxygen was 2 × 10 −5 at pH 6.7 and 7.4. The apparent K m was not significantly altered by the addition of Ca 2+ , and was slightly increased in the presence of N 6 ‐mono‐butyryl cyclic AMP or high K + . These data are consistent with the hypothesis that the availability of oxygen may limit catecholamine synthesis in the intact rat brain.