  We analyze the conductance of the quantum point contact containing large
localized spin J. The additional plateau is formed on a ballistic conductance
staircase if only one propagating channel is rendered conducting. The
conductance value at this plateau is shown to depend strongly on J and decrease
from 3e^2/2h to e^2/h when J increases from 1/2 to infinity, which is in a good
agreement with the experimental observations [D.J. Reilly, et al, Phys. Rev. B
63, 121311 (2001)].
