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Evidence for the Localization of Hydrogen Peroxide‐Stimulated Cyclooxygenase Activity in Rat Brain Mitochondria: A Possible Coupling with Monoamine Oxidase
Author(s) -
Seregi András,
Serfózó Péter,
Mergl Zsuzsanna
Publication year - 1983
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.1471-4159.1983.tb11297.x
Subject(s) - monoamine oxidase , mitochondrion , pargyline , hydrogen peroxide , cyclooxygenase , chemistry , biochemistry , succinate dehydrogenase , enzyme
The distribution of basal and of H 2 O 2‐ stimulated cyclooxygenase activity in the primary fractions of rat brain homogenates and in the subfractions of crude mitochondrial fraction was studied. For comparison, the localization of H 2 O 2‐ generating monoamine oxidase (MAO) as well as that of the mitochondrial marker succinate dehydrogenase (SDH) was also examined. H 2 O 2 was generated by MAO using 5 × 10 −4 M noradrenaline (NA) or 2 × 10 −4 M 2‐phenylethylamine (PEA) as substrates, or by 25 μg glucose oxidase (GOD) per ml in the presence of 1 m M glucose. For nonstimulated (basal) cyclooxygenase, the relative specific activity (RSA) was high in microsomes (1.79) and in the free mitochondria‐containing subfraction of the crude mitochondrial fraction (1.94). Parallel distribution of MAO and H 2 O 2‐ stimulated cyclooxygenase was observed in all fractions studied in the presence of NA. The highest RSA was found in the purified mitochondria for both enzymes (1.85 for MAO and 1.97 for H 2 O 2‐ stimulated cyclooxygenase). The enrichment of SDH (RSA = 2.21) indicated a high concentration of mitochondria in this fraction. The same distribution of H 2 O 2‐ stimulated cyclooxygenase was obtained when, instead of the MAO‐NA system, hydrogen peroxide was generated by GOD in the presence of glucose. H 2 O 2 generated by deamination of NA or PEA by MAO, or during the enzymatic oxydation of glucose by GOD, caused a threefold increase in mitochondrial endoperoxide formation. Indomethacin (2 × 10 4 M ), catalase (50 μg/ml) and pargyline (2 × 10 −4 M ) eliminated the MAO‐dependent mitochondrial synthesis of PG endoperoxides. The GOD‐dependent cyclooxygenase activity of this fraction was abolished by in domethacin or catalase, but not by pargyline. The results show the existence of a mitochondrial cyclooxygenase in brain tissue. The enzyme is sensitive to H 2 O 2 and produces prostaglandin endoperoxides from an endogenous source of arachidonic acid. The identical localization of H 2 O 2‐ producing MAO and H 2 O 2‐ sensitive cyclooxygenase suggests a possible coupling between monoamine and arachidonic acid metabolism.