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PHOTOOXIDATION OF EPINEPHRINE SENSITIZED BY METHYLENE BLUE—EVIDENCE FOR THE INVOLVEMENT OF SINGLET OXYGEN AND OF SUPEROXIDE
Author(s) -
Jahnke Leland S.,
Frenkel Albert W.
Publication year - 1978
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.1978.tb06961.x
Subject(s) - chemistry , adrenochrome , methylene blue , singlet oxygen , superoxide , photochemistry , hydrogen peroxide , azide , superoxide dismutase , catalase , oxygen , epinephrine , reactive oxygen species , medicinal chemistry , catalysis , organic chemistry , biochemistry , enzyme , medicine , photocatalysis , anesthesia
— The photooxidation of epinephrine, sensitized by methylene blue or by chlorophylls, excited with red light, involves the reduction of two molecules of oxygen to hydrogen peroxide per molecule of epinephrine oxidized to adrenochrome. The initial rates of these reactions are not affected by low concentrations of catalase. In 99 mol % D 2 O, rates of methylene blue sensitized photooxidations are accelerated as much as 5.2 times over rates in ordinary water. Azide anion is a more effective inhibitor of this reaction in D 2 O than in H 2 O. Half maximal inhibitions are obtained by 1.3 mM azide in H 2 O and by 0.1 mAf azide in D 2 O. Isotope effects and azide sensitivities point to photooxidation of epinephrine in D 2 O primarily by a singlet oxygen pathway; in H 2 O, non‐singlet oxygen pathways become more predominant. Superoxide dismutase (SOD) markedly inhibits rates of the photooxidations in H 2 O and in D 2 O; about 25% at 10 ‐9 M SOD, and 50% at 10 ‐6 M SOD in H 2 O. In the photooxidation in H 2 O, both by non‐singlet and singlet oxygen mechanisms, the amount of superoxide produced is equivalent to the amount of O 2 consumed in the photooxidation of epinephrine; the superoxide thus formed participates in the oxidation of epinephrine.