The reduction of membrane-bound dopamine beta-monooxygenase in resealed chromaffin granule ghosts. Is intragranular ascorbic acid a mediator for extragranular reducing equivalents?
Wimalasena, Kandatege Wimalasena, D. Shyamali
Wimalasena, Kandatege
Wimalasena, D. Shyamali
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Authors
Wimalasena, Kandatege
Wimalasena, D. Shyamali
Wimalasena, D. Shyamali
Other Names
Wichita State University. Department of Chemistry
Location
Time Period
Advisors
Original Date
Digitization Date
Issue Date
1995-11-17
Type
Article
Genre
Keywords
Comparative Study,Research Support, U.S. Gov't, P.H.S.
Subjects (LCSH)
Ascorbic Acid/metabolism
Ascorbic Acid/pharmacology
Ascorbic Acid/pharmacology
Citation
The Journal of biological chemistry. 1995 Nov 17; 270(46): 27516-24.
Abstract
The role of internal and external reductants in the dopamine beta-monooxygenase (D beta M)-catalyzed conversion of dopamine to norepinephrine has been investigated in resealed chromaffin granule ghosts. The rate of norepinephrine production was not affected by the exclusion of internal ascorbate. The omission of ascorbate from the external medium drastically reduced the norepinephrine production without affecting the net rate of dopamine uptake. In the presence of the external reductant, the internal ascorbate levels were constant throughout the incubation period. The rate of norepinephrine production was not affected when ghosts were resealed to contain the D beta M reduction site inhibitor, imino-D-glucoascorbate. Ghosts incubated with external imino-D-glucoascorbate reduced the norepinephrine production. The weak D beta M reductant, 6-amino-L-ascorbic acid, was found to be a good external reductant for granule ghosts. The outcome of the above experiments was not altered when dopamine was replaced with the reductively inactive D beta M substrate, tyramine. These results and the known topology of membrane-bound D beta M disfavor the direct reduction of the enzyme by the external reductant. Our observations are consistent with the hypothesis that external ascorbate is the sole source of reducing equivalents for D beta M monooxygenation and that internal soluble ascorbate (or dopamine) may not directly reduce or mediate the reduction of membrane-bound D beta M in resealed granule ghosts.
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Publisher
American Society for Biochemistry and Molecular Biology
Journal
Book Title
Series
The Journal of biological chemistry
J. Biol. Chem.
J. Biol. Chem.
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PubMed ID
DOI
ISSN
0021-9258