Crystals formed from a papain digest of rabbit IgG :
the Fc fragment, as discovered by Pr Porter in 1956,
a half century ago
Porter, in 1956, using the proteolytic enzyme papain, found rabbit IgG was cleaved into 3 similarly sized fragments.
Two of these, the Fab fragments, bound to the Ag.
The third fragment crystallized into diamond shaped plates.
Porter first thought it was an artifact, and discarded it.
A few months later O. Kennard, an X-ray crystallographist from the neighbouring lab in Cambridge UK suggested this fragment could be a protein. Porter named it the Fc fragment (for (fragment crystallisable).
Around the same time Edelman at Rockefeller (New York) was deciphering the 4 chain structure of immunoglobulins.
Both received the Nobel Prize for Physiology and Medicine in 1972.