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SCAVENGING OF SINGLET MOLECULAR OXYGEN BY IMIDAZOLE COMPOUNDS: HIGH and SUSTAINED ACTIVITIES OF CARBOXY TERMINAL HISTIDINE DIPEPTIDES and EXCEPTIONAL ACTIVITY OF IMIDAZOLE‐4‐ACETIC ACID
Author(s) -
Hartman Philip E.,
Hartman Zlata,
Ault Katherine T.
Publication year - 1990
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.1751-1097.1990.tb01684.x
Subject(s) - singlet oxygen , histidine , imidazole , carnosine , chemistry , dipeptide , acetic acid , stereochemistry , oxygen , amino acid , organic chemistry , biochemistry
— Singlet molecular oxygen was generated by illumination of phenosafranin in phosphate buffer at pH 7.5. Relative efficiencies of various imidazole compounds to form endoperoxides were assayed by following at 25°C the rate of light‐ and imidazole‐dependent bleaching of N,N‐dimethyl‐4‐nitrosoaniline. Of over 30 imidazole compounds tested, imidazole‐4‐acetic acid, a major catabolite of histamine in mammals, exhibited the highest activity. l ‐Carnosine (β‐alanyl‐ l ‐histidine), a natural dipeptide prevalent in striated muscle of mammals, possessed several properties important for a physiologically significant scavenger of singlet oxygen. On a molar basis, this readily water‐soluble C‐terminal histidine dipeptide reacted with singlet oxygen two‐to four‐fold faster than free L‐histidine and approximately two‐fold faster than the N‐terminal l ‐histidine dipeptides tested. Furthermore scavenging ability of L‐carnosine did not appreciably increase or decrease with time of reaction, in contrast to behaviors exhibited by a number of other imidazole compounds that included some other C‐terminal L‐histidine dipeptides. The fungal metabolite, ergothioneine, blocked singlet oxygen generation by illuminated phenosafranin.