[ Eq(Derivative(x1, t), (1*k28*(k1 + k3*x2)*x1*(1 - k2*x1) + (-1)*k28*k5*x1*x3/(k4 + x4))/k28),
  Eq(Derivative(x2, t), (1*k28*(k6 + k7*x4/(k8 + x4))*x2*(1 - k9*x2) + (-1)*k28*k10*x2)/k28),
  Eq(Derivative(x3, t), (1*k28*k11*x3*x5/((k12 + x5)*(k13 + x4)) + (-1)*k28*k15*x3 + 1*k28*k14)/k28),
  Eq(Derivative(x4, t), (1*k28*k29 + (-1)*k28*k18*x4 + 1*k28*k19*x1*x2/(k20 + x5))/k28),
  Eq(Derivative(x5, t), (1*k28*k21*x1*x3/(k22 + x1) + (-1)*k28*k23*x5)/k28),
  Eq(Derivative(x6, t), ((-1)*k28*k27*x6 + 1*k28*k24)/k28) ]