{ diff(x1, t) = (-1)*k5*x1/k6,
  diff(x2, t) = ((-1)*k7*x1*x2^k8/(k9^k8 + x2^k8) + 1*x21*k15*x3^k16/(k17^k16 + x3^k16) + (-1)*x9*k18*x2^k19/(k20^k19 + x2^k19))/k6,
  diff(x3, t) = (1*k7*x1*x2^k8/(k9^k8 + x2^k8) + (-1)*x21*k15*x3^k16/(k17^k16 + x3^k16) + 1*x9*k18*x2^k19/(k20^k19 + x2^k19))/k6,
  diff(x4, t) = ((-1)*x5*k37*x4^k38/(k39 + x4^k38) + 1*x12*k43*x16^k44/(k45^k44 + x16^k44) + 1*x19*k52*x16^k53/(k54^k53 + x16^k53))/k6,
  diff(x5, t) = (1*x3*k10*x15^k11/(k12^k11 + x15^k11) + (-1)*x18*k46*x5^k47/(k48^k47 + x5^k47))/k6,
  diff(x6, t) = (1*x16*k40*x17^k41/(k42^k41 + x17^k41) + (-1)*x14*k49*x6^k50/(k51^k50 + x6^k50))/k6,
  diff(x7, t) = ((-1)*x6*k13*x7/(k14 + x7) + 1*x14*k31*x8^k32/(k33^k32 + x8^k32))/k6,
  diff(x8, t) = (1*x6*k13*x7/(k14 + x7) + (-1)*x14*k31*x8^k32/(k33^k32 + x8^k32))/k6,
  diff(x9, t) = (-1)*k1*x9/k6,
  diff(x10, t) = ((-1)*x9*k21*x10^k22/(k23^k22 + x10^k22) + (-1)*x1*k24*x1*x10^k25/(k26^k25 + x10^k25) + (-1)*x5*k34*x10^k35/(k36^k35 + x10^k35) + 1*k2*x11)/k6,
  diff(x11, t) = (1*x9*k21*x10^k22/(k23^k22 + x10^k22) + 1*x1*k24*x1*x10^k25/(k26^k25 + x10^k25) + 1*x5*k34*x10^k35/(k36^k35 + x10^k35) + (-1)*k2*x11)/k6,
  diff(x12, t) = (1*x11*k27*x13^k28/(k29^k28 + x13^k28) + (-1)*k30*x12)/k6,
  diff(x13, t) = ((-1)*x11*k27*x13^k28/(k29^k28 + x13^k28) + 1*k30*x12)/k6,
  diff(x14, t) = 0/k6,
  diff(x15, t) = ((-1)*x3*k10*x15^k11/(k12^k11 + x15^k11) + 1*x18*k46*x5^k47/(k48^k47 + x5^k47))/k6,
  diff(x16, t) = (1*x5*k37*x4^k38/(k39 + x4^k38) + (-1)*x12*k43*x16^k44/(k45^k44 + x16^k44) + (-1)*x19*k52*x16^k53/(k54^k53 + x16^k53))/k6,
  diff(x17, t) = ((-1)*x16*k40*x17^k41/(k42^k41 + x17^k41) + 1*x14*k49*x6^k50/(k51^k50 + x6^k50))/k6,
  diff(x18, t) = 0/k6,
  diff(x19, t) = 0/k6,
  diff(x20, t) = ((-1)*x8*k3*x20/(k4 + x20) + 1*k55*x21)/k6,
  diff(x21, t) = (1*x8*k3*x20/(k4 + x20) + (-1)*k55*x21)/k6 }