Abstract
1) The present research has been planed to demonstrate the importance of tryptophan residues on enzyme activity of papain by means of NBS oxidation. 2) About 2 tryptophan residues were oxidized and the first oxidizable tryptophan was important for enzyme activity. 3) The relationship between tryptophan oxidation and enzyme activity for acetylpapain and mercuripapain are quite similar to that for papain. 4) About 1 tryptophan and 3 tyrosine residues in papain were modified by NBS oxidation. However, only 1 tryptophan residue and no tyrosine residue in acetylpapain were oxidized at complete inactivation. 5) The acetylation of tyrosine in papain prevented the tyrosine from oxidizing by NBS. 6) SH group and histidine residues in papain were not affected by NBS oxidation. 7) These results indicate that the modification of a tryptophan residue by NBS oxidation causes loss of the enzyme activity.
