An anti-proton has the same mass as a proton, which is much greater than the mass of the electron. An electron and an anti-proton cannot interact to anihilate one another.
Lonesome in Massachussets: How about a neutron and an anti-proton? Do you happen to know of a table of subatomic particles that shows which particles and anti-particles will annihilate if they come into contact?
Good question, Mind-numbed Robot. I had never considered it before.