x1 = Arg
x2 = Fe3__enos
x3 = Fe3__Arg
x4 = Fe2
x5 = Fe2__Arg
x6 = Fe3__NO
x7 = NO
x8 = Fe2__NO
x9 = Fe3__NOHA
x10 = NOHA
x11 = Fe2__NOHA
x12 = O2
x13 = Fe3__O2__Arg
x14 = Fe3__O2__NOHA
x15 = Citrulline