[ Eq(Derivative(x1, t), k1*k4**k5/(k4**k5 + x3**k5) - k2*x1/(k3 + x1)),
  Eq(Derivative(x2, t), k7*x1 + k11*x3 - (k8*x2/(k9 + x2) + k10*x2)),
  Eq(Derivative(x3, t), k10*x2 - k11*x3) ]