[ Eq(Derivative(x1, t), ((-1)*k23*(k1*x1 + k2*x5*x1/(k3 + x1)) + 1*k23*k17 + (-1)*k23*k19*x1)/k23),
  Eq(Derivative(x2, t), (1*k23*(k1*x1 + k2*x5*x1/(k3 + x1)) + (-1)*k23*(k4*x2*x9 - k5*x3) + 1*k23*k15*x6 + 1*k23*k6*x5 + (-1)*k23*(k11*x2*x8 - k12*x10))/k23),
  Eq(Derivative(x3, t), (1*k23*(k4*x2*x9 - k5*x3) + (-1)*k23*(k9*x3 - k10*x4))/k23),
  Eq(Derivative(x4, t), (1*k23*(k9*x3 - k10*x4) + (-1)*k23*k7*x13*x4/(k8 + x4))/k23),
  Eq(Derivative(x5, t), (1*k23*k7*x13*x4/(k8 + x4) + (-1)*k23*(k16*x5*x8 - k12*x6) + (-1)*k23*k6*x5)/k23),
  Eq(Derivative(x6, t), (1*k23*(k16*x5*x8 - k12*x6) + (-1)*k23*k15*x6)/k23),
  Eq(Derivative(x7, t), (1*k23*k15*x6 + 1*k23*k6*x5)/k23),
  Eq(Derivative(x8, t), ((-1)*k23*(k16*x5*x8 - k12*x6) + 1*k23*k15*x6 + (-1)*k23*(k11*x2*x8 - k12*x10) + 1*k23*k13*x10*x11/(k14 + x10) + 1*k23*k21 + (-1)*k23*k22*x8)/k23),
  Eq(Derivative(x9, t), ((-1)*k23*(k4*x2*x9 - k5*x3) + 1*k23*k18 + (-1)*k23*k20*x9)/k23),
  Eq(Derivative(x10, t), (1*k23*(k11*x2*x8 - k12*x10) + (-1)*k23*k13*x10*x11/(k14 + x10))/k23),
  Eq(Derivative(x11, t), 0/k23),
  Eq(Derivative(x12, t), 1*k23*k13*x10*x11/(k14 + x10)/k23),
  Eq(Derivative(x13, t), 0/k23) ]