Structure of tetanus toxin: the arrangement of papain digestion products within the heavy chain-light chain framework of extracellular toxin.

Upon digestion with papain, single chain intracellular tetanus toxin was completely converted to the extracellular form of the toxin, which consists of two disulfide-linked polypeptide chains (heavy chain and light chain of tetanus toxin). A portion of the material was degraded further by papain to yield the two major protein fragments, B and C, respectively, previously identified after digesting extracellular tetanus toxin with this enzyme. Thus it may be concluded that the order of release of these of these fragments from the intracellular toxin does not provide a clue as to their position within the original molecule. However, N-terminal analysis of the two fragments in conjunction with recent N-terminal data on tetanus toxin itself clearly indicated that fragment B of tetanus toxin contains the light chain polypeptide and the N-terminal portion of the heavy chain, whereas fragment C is derived from the C-terminal portion of the heavy chain.