bNO2 = 81000 s21 k13NO = 1600 s21 Vm = 320 mMs21 Km = 50 mM k14NO = 0.0002 s21 k15NO = 100 mM21s21 k16NO = 1.21 mM21s21 k17NO = 66 mM21s21 a N2O3+H2ORproducts GSSG+NADPH+H+R2GSH+NADP+ Cu+ GSNORK GSSG+NO CcOx+NORCcOX.NO FeLn+NORFeLnNO FeLnNO+GSHRGSNO+FeLn GSH+O22RK GSSG+products a k17bNO = 0.0002 mM21s21 Same as k11NO doi:10.1371/journal.pone.0002249.t001 mBax for the transition from bistability to monostability is called a limit point. We explored how the inclusion of NO reactions affects these findings. The limit point value of the Bax degradation rate for monostable cell survival is found to remain unchanged for the range 103#0#104 mM. However, it decreases to 0.098 s21 for 0 = 102 mM and 0.096 s21 for 0 = 0 mM in the present model. The model again predicts that N2O3 is not influential when the GSH level is sufficiently high in the cell. Roles of non-heme iron complexes and GSH in apoptotic response. One of the important anti-apoptotic effects of NO is presumed to occur via its ability to react with non-heme iron complexes to form FeLnNO. These species inhibit caspases by S-nitrosating the catalytic cysteine in the active site of these enzymes. The results are presented in Effects of NO on Apoptosis 23316025 apoptotic effects is not well established. In the present study, we assume that the pro-apoptotic effect of NO occurs via formation of ONOO2, as has been suggested from a large number of experimental studies both in vitro and in vivo. Experimental studies suggest that ONOO2 may induce the opening of mitochondrial permeability transition pores and subsequent cyt c ABT-267 site release from mitochondria. The possible mechanisms of cyt c release from mitochondria are diverse and controversial. In our model, we assume that cyt c release is mediated by activation of MPTPs, independent of Bax channel formation on mitochondria. The complex that forms the 
MPTPs is called mitochondrial permeability transition pore complex. The complex consists of peripheral benzodiazepine receptor, cyclophilin D, adenine nucleotide translocator, voltage-dependent anion channel, and other proteins. ANT is proposed to be converted from a specific transporter to a non-specific pore which then releases cyt c into the cytoplasm and subsequently induces apoptosis. It has been suggested that ONOO2 acts on PTPC, specifically on ANT, to convert it to a non-specific pore . We represent this Effects of NO on Apoptosis Discussion We present here the results from simulations that incorporate the main chemical interactions of NO with components of the apoptotic interactions network, with the goal of shedding light on the dichotomous effects of NO on apoptosis. Based on previously published studies, we considered N2O3 and FeLnNO to be antiapoptotic and ONOO2 pro-apoptotic. The results predict that cell survival or apoptosis is determined by a complex interplay among these reactive NO species and GSH. We observed that relative concentrations of anti-apoptotic and pro-apoptotic species determine the ultimate cell fate at late time 19286921 points. Interestingly, transient apoptotic effects were observed under specific conditions. These intriguing findings point to the importance of the timing of NO production and apoptotic stimuli in determining the actual anti- or pro-apoptotic effect, even if steady state conditions favor cell survival, in agreement with our previous observations. Another interesting effect we observed in our simulations was the time shift/delay in the onset of apoptosis in the presen
