Immunochemistry of Tetanus Toxin

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Abstract
The tyrosyl residues of tetanus toxin can be specifically nitrated by tetranitromethane. The introduction of NO2 groups into the toxin molecule is followed by a rapid decrease in toxicity. Although tryptophyl residues are differently involved and some aggregation occurs, these two phenomena do not take any significant part in the toxicity loss. The immunological reactivity in vitro is preserved. However, it is modified when a certain amount of NO2 groups have been introduced. The thus‐formed derivative no longer gives a reaction of identity with the native toxin. Furthermore, when a sufficiently large number of NO2 groups have been introduced, two lines of precipitation are seen. Antisera raised in rabbits with a few nitro‐derivatives of the toxin exhibit a low avidity. Precipitating power with pure toxin of these antisera is lower than with a normal antitetanus serum. The capability of tetanus toxin to give rise to neutralizing antibodies is not impaired until 33 NO2 groups have been introduced, then it gradually decreases until it finally disappears. Modification of the toxin by nitration allowed us to discriminate three groups of determinants. In particular, the results presented are further substantiated by those given by 3‐aminotyrosyl derivatives of tetanus toxin.