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3232578 
Journal Article 
Reactions of PTIO and carboxy-PTIO with (NO)-N-center dot, (NO2)-N-center dot, and O-2(center dot) 
Goldstein, S; Russo, A; Samuni, A 
2003 
Yes 
Journal of Biological Chemistry
ISSN: 0021-9258
EISSN: 1083-351X 
278 
51 
50949-50955 
WOS:000187206300016 
Nitronyl nitroxides, such as derivatives of 2- phenyl 4,4,5,5,- tetramethylimidazoline- 1- oxyl 3- oxide ( PTIOs), react with (.) NO to form the
corresponding imino nitroxides ( PTIs) and (.) NO2. PTIOs are considered as monitors of (NO)-N-.,
stoichiometric sources of (NO2)-N-., biochemical and physiological effectors, specific tools for
the elimination of (NO)-N-., and potential therapeutic agents. However, a better understanding of
the chemical properties of PTIOs, especially following their reaction with (NO)-N-., is necessary
to resolve many of the reported discrepancies surrounding the effects of PTIOs and to better
characterize their potential therapeutic activity. We have generated electrochemically the
oxidized and reduced forms of PTIO and carboxy- PTIO ( C- PTIO), characterized their absorption
spectra, and determined the reduction potentials for the oxoammonium/ nitroxide and nitroxide/
hydroxylamine couples. The rate constants for the reaction of (NO2)-N-. with PTIO and C- PTIO to
form the corresponding oxoammonium cations ( PTIO (+) s) and nitrite were determined to be ( 1.5
- 2) x 10(7) M-1 s(-1). We have also shown that the reactions of PTIO(+)s with (NO)-N-. form
PTIOs and NO2-. The rate constants for these reactions are approximately 30- fold higher than
those for the reactions of PTIOs with (NO)-N-. or O-2. The present results show that ( i) the
reaction of PTIOs with (NO)-N-. forms solely PTIs and NO2- where [NO2-]/[ PTI] varies between 1
and 2 depending on the steady- state concentrations of (NO)-N-.. Consequently, quantitation of
(NO)-N-. is valid only at sufficiently low fluxes of (NO)-N-.; ( ii) the reaction of PTIOs with
(NO)-N-. can be used as a valid source of (NO2)-N-. only when the latter is effectively scavenged
by an appropriate reductant; and ( iii) the formation of peroxynitrite cannot be efficiently
inhibited by PTIOs even under relatively low fluxes of (NO)-N-. and O-2. and millimolar levels of
PTIOs.