{ diff(x1, t) = 0,
  diff(x2, t) = ((-1)*k1*x2/(k2 + x2) + (-1)*k6*x2/(k7 + x2) + (-1)*k8*x2/(k9 + x2))/k10,
  diff(x3, t) = (1*k1*x2/(k2 + x2) + (-1)*k3*x3*x4*k10*k10)/k10,
  diff(x4, t) = ((-1)*k3*x3*x4*k10*k10 + 1*k4*(k5 - x4)*k10)/k10,
  diff(x5, t) = 1*k3*x3*x4*k10*k10/k10,
  diff(x6, t) = 1*k6*x2/(k7 + x2)/k10,
  diff(x7, t) = 1*k8*x2/(k9 + x2)/k10 }