  We study the vertex function of two vector and one axial-vector operators in
the soft-wall holographic model of QCD. In particular, we discuss the possible
relation, introduced by Son and Yamamoto, between the structure function $w_T$
describing such a vertex when one of the two vector currents represents an
on-shell soft photon and the the two-point $\Pi_\perp^{VV}-\Pi_\perp^{AA}$
correlation function.
