x1 = FeIII
x2 = FeII
x3 = FeII_O2
x4 = FeIII_star
x5 = FeII_star
x6 = FeII_star_O2
x7 = FeIII_NO
x8 = FeII_NO
x9 = NADPH
x10 = O2
x11 = citrulline
x12 = NO3
x13 = NO
x14 = NADPplus
x15 = FeIII_t