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PHOTOGENERATION OF SUPEROXIDE and DECARBOXYLATED PEPTIDE RADICALS BY CARBOQUONE, MITOMYCIN C and STREPTONIGRIN. AN ELECTRON SPIN RESONANCE and SPIN TRAPPING STUDY
Author(s) -
Carmichael Alasdair J.,
Samuni Amram,
Riesz Peter
Publication year - 1985
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.1751-1097.1985.tb03616.x
Subject(s) - chemistry , radical , spin trapping , photochemistry , electron paramagnetic resonance , superoxide , decarboxylation , peptide , solvated electron , organic chemistry , radiolysis , nuclear magnetic resonance , catalysis , biochemistry , physics , enzyme
— Visible light (405–615 nm) excitation of carboquone, mitomycin C, and streptonigrin dissolved in dimethylsulfoxide in the presence of oxygen generates superoxide anion radicals (O 2 − ). The quantum yields for these reactions range from 4.2 times 10 −2 (carboquone, λ= 615 ± 10 nm) to 7.3 times 10 −6 (streptonigrin, λ=545 ± 10 nm). O 2 − radicals were spin trapped with 5,5‐dimethyl‐1‐pyrroline‐1‐oxide (DMPO) and identified by electron spin resonance (ESR). The efficiency of DMPO to spin trap O 2 − in dimethylsulfoxide was determined and indicated that 91% of the O 2 − present in dimethylsulfoxide is trapped by DMPO. The oxidation of the photoexcited drug molecules occurs via a direct electron transfer to dissolved oxygen in solution. Ultraviolet irradiation (λ= 313 ± 10 nm) of the aminoquinone drug solutions (80% H 2 O, 20% dimethylsulfoxide) in the presence of peptides results in the decarboxylation of the peptides. In this case the photoexcited drugs are reduced, abstracting an electron from the C‐terminal carboxyl group of the peptides. The reaction is specific to the C‐terminal amino acid of the peptide. The decarboxylated peptide radicals were spin trapped with 2‐methyl‐2‐nitrosopropane (MNP) and identified by ESR.