Chemistry Letters
Online ISSN : 1348-0715
Print ISSN : 0366-7022
ISSN-L : 0366-7022
Volume 38 , Issue 4
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  • Masahiro Kohno, Emiko Sato, Noriko Yaekashiwa, Takayuki Mokudai, Yoshi ...
    2009 Volume 38 Issue 4 Pages 302-307
    Published: April 05, 2009
    Released: February 28, 2009
    We investigated the hypoxanthine (HPX)–xanthine oxidase (XOD) reaction by examining the chemiluminescence (CL) response mediated by a luminol analog, 8-amino-5-chloro-7-phenylpyrido[3,4-d]pyridazine-1,4-(2H,3H)-dione sodium salt (L-012). It was found that addition of a high concentration of dimethyl sulfoxide (DMSO), a potent OH scavenger, could not completely reduce the CL response. This result suggests the existence of an unknown reactive oxygen intermediate other than O2−• and OH. We further examined the HPX–XOD reaction and the nicotinamide adenine dinucleotide phosphate (NADPH) oxidation reaction by applying an electron spin resonance (ESR) spin-trapping method. In both reaction systems, similar responses were observed. That is, addition of DMSO increased the formation of 5,5-dimethyl-1-pyrroline N-oxide (DMPO) –OOH in a concentration-dependent manner. This indicates that scavenging of OH increases the detected O2−• level, further suggesting the existence of an intermediate oxygen species derived from O2−• and OH. One candidate for this species is HOOOH, presumably formed in the following way.

    O2−• + H+ + OH →HOOOH
    In two typical enzyme reaction systems producing reactive oxygen species, hypoxanthine–xanthine oxidase and nicotinamide adenine dinucleotide phosphate oxidation, we postulate the existence of an intermediate oxygen species derived from O2−• and OH, as in the following reaction. O2−• + H+ + OH → HOOOH Fullsize Image