Biological activity of heated diphtheria toxin.
Diphtheria toxin splits into two fragments when heated at 100 C for 10 min in a phosphate buffer. The separated fragments have molecular weights of 24,000 and 39,000, respectively. These molecular weights are similar to those of the A and B fragments found in diphtheria toxin preparations after thiol reduction. Since the separation of toxin into fragments is not complete, it is likely that only nicked toxin molecules having a cleaved peptide bond are split by heating. When toxin is suspended in phosphate buffer at pH 6.4, the B-like fragment precipitates, but at pH 7.8 it does not. Heated toxin is unable to intoxicate sensitive cells or cause a necrodermal response in animals. Fragment A produced by heating is active in inhibiting cell-free protein synthesis. It is able to intoxicate both HeLa and L cells when the uptake of the fragment is facilitated by addition of polyornithine to the cultures. Fragment B produced by heating is involved with binding to the cell surface. It is able to delay the action of toxin on KB cell cultures preincubated with fragment B.
D000818:Animals; D002247:Carbon Isotopes; D002277:Carcinoma; D002460:Cell Line; D002474:Cell-Free System; D003353:Corynebacterium diphtheriae / Q000032:analysis; D004167:Diphtheria Toxin / Q000032:analysis / Q000302:isolation & purification / Q000494:pharmacology*; D004591:Electrophoresis, Polyacrylamide Gel; D006367:HeLa Cells / Q000378:metabolism; D006358:Hot Temperature; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007739:L Cells / Q000378:metabolism; D008099:Liver; D051379:Mice; D008970:Molecular Weight; D009062:Mouth Neoplasms; D009363:Neoplasm Proteins / Q000096:biosynthesis; D009952:Ornithine / Q000494:pharmacology; D010649:Phenylalanine / Q000378:metabolism; D011108:Polymers; D014176:Protein Biosynthesis; D051381:Rats; D012270:Ribosomes / Q000378:metabolism
D002247:Carbon Isotopes; D004167:Diphtheria Toxin; D009363:Neoplasm Proteins; D011108:Polymers; D010649:Phenylalanine; D009952:Ornithine