{ diff(x1, t) = ((-1)*k1*k3*x1/(k2 + x1) + 1*k1*k11*x5*k19/((x5 + k12)*(k19 + k13)))/k1,
  diff(x2, t) = (2*k1*k3*x1/(k2 + x1) + (-1)*k1*k4*x2*k19/((x2 + k5)*(k19 + k6)) + (-1)*k1*k15*x2/(k14 + x2))/k1,
  diff(x3, t) = (1*k1*k4*x2*k19/((x2 + k5)*(k19 + k6)) + (-1)*k1*k8*x3/(k7 + x3))/k1,
  diff(x4, t) = (1*k1*k8*x3/(k7 + x3) + (-1)*k1*k10*x4/(k9 + x4) + (-1)*k1*k17*x4/(k16 + x4))/k1,
  diff(x5, t) = (3/5*k1*k10*x4/(k9 + x4) + (-1)*k1*k11*x5*k19/((x5 + k12)*(k19 + k13)))/k1,
  diff(x6, t) = 0,
  diff(x7, t) = 0 }