  Recent experiments by Mertz et al (Phys. Rev. B55, 9160, 1997) demonstrated
that the loss of superconductivity upon Pr doping is associated with the change
of the character of the oxygen holes from $p_{\sigma}$ to $p_{\pi}.$ This
experiment sheds new light onto the long-standing problem of $T_{c}$
suppression by Pr, and helps to rule out a number of theoretical models,
leaving only those which predict such a transfer of the O holes. To distinguish
between the two models that do predict such an effect, one has to access the
ratio of the planar and axial character of the holes in both models. We do so
in this paper.
