PHOTOGENERATION OF SUPEROXIDE and DECARBOXYLATED PEPTIDE RADICALS BY CARBOQUONE, MITOMYCIN C and STREPTONIGRIN. AN ELECTRON SPIN RESONANCE and SPIN TRAPPING STUDY

Alasdair J. Carmichael*, Amram Samuni, Peter Riesz

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

31 Scopus citations

Abstract

Visible light (405–615 nm) excitation of carboquone, mitomycin C, and streptonigrin dissolved in dimethylsulfoxide in the presence of oxygen generates superoxide anion radicals (O2). 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). O2 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 O2 in dimethylsulfoxide was determined and indicated that 91% of the O2 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% H2O, 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.

Original languageEnglish
Pages (from-to)635-642
Number of pages8
JournalPhotochemistry and Photobiology
Volume41
Issue number6
DOIs
StatePublished - May 1985
Externally publishedYes

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