Electronic structures of C-60 and its endohedral complexes with Li, Na, K, Be, Mg, Ca, La, B, and Al have been calculated by means of density functional methodology. The electronic distributions have been analyzed from the point of view of the guest-host electron transfer. Alkali metals and Al have been found to donate their outermost electron to the fullerene cage. There is no electron transfer for Be, while for B, Mg, Ca, and La the transfer is only partial. For the entire series, ionization potentials and electron affinities have been calculated which are in excellent agreement with the few values known from experiments. The results are consistent with the donor-acceptor properties of the guest atom.