  We analyze the observed shell gaps in N=Z nuclei determined from the binding
energy differences. It is found that the shell gaps can be described by the
combined contributions from the single-particle level spacing, the like-nucleon
pairing, and the proton-neutron pairing interaction. This conclusion is
consistent with that of Chasman in Phys. Rev. Lett. 99 (2007) 082501. For the
double-closed shell N=Z nuclei, the single-particle level spacings calculated
with Woods-Saxon potential are very close to those obtained by subtracting the
nn pairing interaction from the observed shell gap. For the sub-closed or
non-closed shell N=Z nuclei, the pn pairing interaction is shown to be
important for the observed shell gaps.
