  Motivated by measurements of the flavor singlet axial coupling constant of
the nucleon in polarized deep inelastic scattering we study the contribution of
instantons to OZI violation in the axial-vector channel. We consider, in
particular, the f_1-a_1 meson splitting, the flavor singlet and triplet axial
coupling of a constituent quark, and the axial coupling constant of the
nucleon. We show that instantons provide a short distance contribution to OZI
violating correlation functions which is repulsive in the f_1 meson channel and
adds to the flavor singlet three-point function of a constituent quark. We also
show that the sign of this contribution is determined by positivity arguments.
We compute long distance contributions using numerical simulations of the
instanton liquid. We find that the iso-vector axial coupling constant of a
constituent quark is (g_A^3)_Q=0.9 and that of a nucleon is g_A^3=1.28, in good
agreement with experiment. The flavor singlet coupling of a quark is close to
one, while that of a nucleon is suppressed, g_A^0=0.77. However, this number is
larger than the experimental value g_A^0=(0.28-0.41).
