Since 1978, List Labs products are unsurpassed in quality, consistency, and reliability for the success of your research and development project! Diphtheria toxin, secreted by certain strains of Corynebacterium diphtheriae, catalyzes the ADP-ribosylation of eukaryotic aminoacyl-transferase II (EF-2) using NAD resulting in toxicity toward eukaryotic organisms. It is synthesized and excreted as a proenzyme, of 58 kDa. For its enzymatic activity, the toxin must undergo two covalent alterations. First, mild proteolysis forming “nicked toxin,” which is inactive and consists of two major fragments, A and B, linked by a disulfide bond. Reduction of the nicked toxin with thiols releases the N-terminal A fragment (21 kDa) which is enzymatically active. Diphtheria toxin is produced in the native strain and is offered as "unnicked". Following trypsin treatment and reduction with dithiothreitol, diphtheria toxin from List Labs exhibits high specific activity.