α-Bungarotoxin labelled with

125

I was obtained by chloramine-T method. It was purified by the use of sephadex G-25 chromatography. The results were as the following: specific activity 90~100Ci/mmol

labelling rate 50%

protein recover 65% and free iodine content less than 3%. The biological experiment showed that the structure and the activity of

125

I-α-Bungarotoxin have no significant change.