  We present angle resolved photoemission (ARPES) data on Na-doped
Ca$_2$CuO$_2$Cl$_2$. We demonstrate that the chemical potential shifts upon
doping the system across the insulator to metal transition. The resulting low
energy spectra reveal a gap structure which appears to deviate from the
canonical $d_{x2-y2} ~ |cos(k_x a)-cos(k_y a)|$ form. To reconcile the measured
gap structure with d-wave superconductivity one can understand the data in
terms of two gaps, a very small one contributing to the nodal region and a very
large one dominating the anti-nodal region. The latter is a result of the
electronic structure observed in the undoped antiferromagnetic insulator.
Furthermore, the low energy electronic structure of the metallic sample
contains a two component structure in the nodal direction, and a change in
velocity of the dispersion in the nodal direction at roughly 50 meV. We discuss
these results in connection with photoemission data on other cuprate systems.
