[ Eq(Derivative(x10, t), 0),
  Eq(Derivative(x11, t), 0),
  Eq(Derivative(x12, t), 0),
  Eq(Derivative(x1, t), k1*x7*x2/(k8 + x2) - k2*x1/(k8 + x1)),
  Eq(Derivative(x3, t), (k5 + x3)*x4/(k9 + x4) - k4*x1*x3/(k9 + x3) - k7*x3*x5/(k9 + x3)),
  Eq(Derivative(x5, t), k6*x7*x6/(k9 + x6) - k3*x3*x5/(k9 + x5)),
  Eq(Derivative(x8, t), (-x8)*1/5),
  Eq(Derivative(x9, t), (-x9)*1/2) ]