C. Salet et al., SINGLET OXYGEN PRODUCED BY PHOTODYNAMIC-ACTION CAUSES INACTIVATION OFTHE MITOCHONDRIAL PERMEABILITY TRANSITION PORE, The Journal of biological chemistry, 272(35), 1997, pp. 21938-21943
We have studied the effects of singlet oxygen produced by photodynamic
action on the cyclosporin A-sensitive permeability transition (PT) in
isolated rat liver mitochondria. Mitochondria were incubated with 3 m
u M hematoporphyrin and irradiated at 365 nm with a fluence rate of 25
watts/m(2). For short durations of irradiation (60 s) the adenine nuc
leotide translocase was inactivated, but mitochondria retained their a
bility to form a proton electrochemical gradient and accumulated Ca2and P-i at the same rate as non-irradiated controls, Strikingly, howev
er, the oxidative effects of photodynamic action prevented opening of
the PT pore which is normally induced by Ca2+ plus P-i or by treatment
with diethyl pyrocarbonate (a histidine reagent) or diamide (a thiol
oxidant), We show that the most likely targets for photodynamic action
are critical histidines that undergo degradation. Irradiated, hematop
orphyrin-loaded mitochondria treated with diethyl pyrocarbonate or dia
mide still undergo the PT when treated with phenylarsine oxide, which
reacts with a critical dithiol involved in pore modulation (Petronilli
, V,, Costantini, P,, Scorrano, L., Colonna, R,, Passamonti, S,, and P
ernardi, P, (1994) J, Biol. Chem. 269, 16638-16642), These data sugges
t (i) that the dithiol cysteines are not oxidized by photodynamic acti
on, but rather became inaccessible to oxidants; and (ii) that irradiat
ion of hematoporphyrin-loaded mitochondria does not lead to pore denat
uration, but rather to site-selective inactivation of discrete pore fu
nctional domains.