x1 = MAPK
x2 = MAPKMEKpp
x3 = MAPKp
x4 = MAPKPH
x5 = MAPKpMAPKPH
x6 = MAPKpMEKpp
x7 = MAPKpp
x8 = MAPKppMAPKPH
x9 = MEK
x10 = MEKp
x11 = MEKPH
x12 = MEKpMEKPH
x13 = MEKpp
x14 = MEKppMEKPH
x15 = MEKpRAFp
x16 = MEKRAFp
x17 = RAF
x18 = RAFK
x19 = RAFp
x20 = RAFPH
x21 = RAFpRAFPH
x22 = RAFRAFK