{ diff(x1, t) = (1*k33*k21 + 1*k33*k22*x1 + (-1)*k33*k23*x2/(k2 + x2)*x1 + (-1)*k33*k24*x7/(k4 + x7)*x5/(k5 + x5)*x1)/k33,
  diff(x2, t) = (1*k33*k25*x1^k7/(k8^k7 + x1^k7)*x7^k10/(k4^k10 + x7^k10)*x6 + (-1)*k33*k26*x2)/k33,
  diff(x3, t) = (1*k33*k27*x2 + (-1)*k33*k28*x3)/k33,
  diff(x4, t) = -1/1000*k34*(k29*x3^3/(k12^3 + x3^3)*x4^k18/(k19^k18 + x4^k18) - k30*x5/(k14 + x5))/k34,
  diff(x5, t) = (1/100*k34*(k29*x3^3/(k12^3 + x3^3)*x4^k18/(k19^k18 + x4^k18) - k30*x5/(k14 + x5)) + -1/20*k33*k31*x5/(k16 + x5) + 1/20*k33*k32)/k33 }