Nitration of Tyrosine Residues in the Pancreatic Trypsin Inhibitor with Tetranitromethane

Nitration of pancreatic trypsin inhibitor with tetranitromethane affords a mono‐and a disubstituted derivative which was shown by sequential analysis to contain nitrotyrosine in position 10 and in positions 10 and 21, respectively. Both retain full trypsin inhibitor activity. Measurements of optical rotatory dispersion in the 230 nm region indicate that the secondary structure of the protein is unaffected by nitration. The nitrated derivatives exhibit a conformation‐dependent side‐chain Cotton effect in the region of nitroaromatic absorption. No such Cotton effect is shown by a nitrotyrosine‐containing pentadecapeptide isolated from the tryptic digest from the nitrated and oxidized inhibitor.