[ Eq(Derivative(x1, t), ((-1)*k15*(k1*x1 + k2*x5*x1/(k3 + x1)) + 1*k15*k11 + (-1)*k15*k13*x1)/k15),
  Eq(Derivative(x2, t), (1*k15*(k1*x1 + k2*x5*x1/(k3 + x1)) + (-1)*k15*(k4*x2*x7 - k5*x3) + 1*k15*k6*x5)/k15),
  Eq(Derivative(x3, t), (1*k15*(k4*x2*x7 - k5*x3) + (-1)*k15*(k9*x3 - k10*x4))/k15),
  Eq(Derivative(x4, t), (1*k15*(k9*x3 - k10*x4) + (-1)*k15*k7*x8*x4/(k8 + x4))/k15),
  Eq(Derivative(x5, t), (1*k15*k7*x8*x4/(k8 + x4) + (-1)*k15*k6*x5)/k15),
  Eq(Derivative(x6, t), 1*k15*k6*x5/k15),
  Eq(Derivative(x7, t), ((-1)*k15*(k4*x2*x7 - k5*x3) + 1*k15*k12 + (-1)*k15*k14*x7)/k15),
  Eq(Derivative(x8, t), 0/k15) ]