Cytochrome b561 and the Maintenance of Redox Poise in Secretory Vesicles
The membranes of a variety of secretory vesicles contain an electron transfer system which supports redox reactions catalyzed by enzymes contained within the vesicles. These enzymes include two important monooxygenases, dopamine ß-hydroxylase and peptide amidating monooxygenase. Dopamine ßhydroxylase, responsible for the biosynthesis of norepinephrine and epinephrine, is found in catecholamine-storing vesicles such as the chromaffin vesicles of the adrenal medulla. Peptide amidating monooxygenase, responsible for the α-amidation of peptide hormones, is found in peptide-storing vesicles such as those in the pituitary and gut. Both monooxygenases use ascorbic acid to reduce the second atom of molecular oxygen to water. While oxygen will diffuse across the secretory vesicle membrane, ascorbate will not. It is to maintain intravesicular ascorbate that the secretory-vesicle membrane has an electron transfer system.
KeywordsElectron Transfer Electron Flow Secretory Vesicle Cytochrome B561 Ascorbate Oxidase
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