  Saturation of small-x gluons in a nucleus, which has the form of transverse
momentum broadening of projectile gluons in pA collisions in the nuclear rest
frame, leads to a modification of the parton distribution functions in the beam
compared with pp collisions. The DGLAP driven gluon distribution turns out to
be suppressed at large x, but significantly enhanced at x<<1. This is a high
twist effect. In the case of nucleus-nucleus collisions all participating
nucleons on both sides get enriched in gluon density at small x, which leads to
a further boosting of the saturation scale. We derive reciprocity equations for
the saturation scales corresponding to a collision of two nuclei. The solution
of these equations for central collisions of two heavy nuclei demonstrate a
significant, up to several times, enhancement of Q_{sA}^2, in AA compared with
pA collisions.
