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