  The recent suggestion of a vanishing flavor-singlet axial charge of nucleon
due to a nontrivial vacuum structure is further amplified. A perturbative QCD
discussion, applicable for the heavy quark contributions, relates it to the
physics of the decoupling theorem. It is also shown that $g_{A}^{0}\simeq 0$
leads to a negative $\eta'$-meson-quark coupling, which has been found to be
compatible with the chiral quark model phenomenology.
