Rodney Robert Porter (1917-1985) was awarded half the 1972 Nobel Prize in Physiology or Medicine for his discoveries concerning the chemical structure of antibodies. Using papain, an enzyme that degrades proteins, Porter cleaved an antibody into fragments which he then examined to determine their structure. Working separately, fellow Nobel Prize winner Gerald M. Edelman found that the antibody was made of different groups or â€œchainsâ€ of amino acids that were either light (about 210 amino acids) or heavy (about 550 amino acids). Porter then established that an antibody is made of two light and two heavy chains of amino acids. Porter later studied each chain separately, while Edelman worked on the whole antibody. By 1969, Porter and Edelman had determined the complete structure of the antibody, showing that it is made of more than 1,300 amino acids.