  The correlator of vector and nonsinglet axial-vector currents in the external
electromagnetic field is calculated within the instanton liquid model of QCD
vacuum. In general the correlator has two Lorentz structures: longitudinal w_L
and transversal w_T with respect to axial-vector index. Within the instanton
model the saturation of the anomalous w_L structure is demonstrated. It is
known that in the chiral limit the transversal structure w_T is free from
perturbative corrections. In this limit within the instanton model we calculate
the transversal invariant function w_T at arbitrary momentum transfer, q, and
show the absence of power corrections to this structure at large q^2. Instead
there arise the exponential corrections to w_T at large q^2 reflecting nonlocal
properties of QCD vacuum. The slope of w_T at zero virtuality, the QCD vacuum
magnetic susceptibility of the quark condensate and its momentum dependence are
estimated.
