  The QCD + QED axial anomaly low-energy theorems are applied to estimate the
accuracy of an instanton vacuum - based chiral quark model. The low-energy
theorems give an exact relation between the matrix elements of the gluon and
photon parts of the QCD + QED axial anomaly operator equation. The matrix
elements between vacuum and two photon states and between vacuum and two gluon
states are calculated for arbitrary N_f. It is shown that this model does
satisfy the low-energy theorems with an accuracy of $\sim 17%$. We estimate
also the contribution of the nonperturbative conversion of gluons into photons
to the decay $\eta ' \rightarrow 2 \gamma$ and compare with experimental data.
