{ diff(x1, t) = 1*k22*(k1 - k2*x1 - k3*x2^k13*x1/(k12^k13 + x2^k13) + (k4 + k5*x1^k7/(k6^k7 + x1^k7))*(x3 - x1) - (k8 + k9*k10^k11/(k10^k11 + x1^k11))*x1)/k22,
  diff(x2, t) = 1*k22*((k14 + k15*(x1/200)^k17/((x1/200)^k17 + k16^k17))*(1 - x2) - (k18 + k19*k20^k21/(x2^k21 + k20^k21))*x2)/k22,
  diff(x3, t) = 1*k22*(k1 - k2*x3 - k3*x2^k13*x3/(k12^k13 + x2^k13))/k22 }