{ diff(x1, t) = (1*k16*k8 + (-1)*k16*k9*x3*x1/(k10 + x1) + (-1)*k16*k15*x1)/k16,
  diff(x2, t) = (1*k16*x1/(k7 + x1)*k3*(1 - x2)/(k11 + 1 - x2) + (-1)*k16*k4*x2/(k12 + x2))/k16,
  diff(x3, t) = (1*k16*x2*k5*(1 - x3)/(k13 + 1 - x3) + (-1)*k16*k6*x3/(k14 + x3))/k16 }