抄録
The reactive sulfhydryl group of stem bromelain [EC 3. 4. 4. 24] was first blocked with tetrathionate, and then the enzyme was allowed to react with molar excess of tetranitromethane or N-acetylimidazole. The number of nitrated or acetylated tyrosyl residues increases as the molar ratio of modifying reagent to the enzyme protein increases, but it reaches a plateau at around 8 to 9 residues per molecule. This result is in good agreement with the previous conclusion obtained from spectro-photometric titration studies that 9 tyrosyl residues of stem bromelain are in the exposed state. When the enzymatic activity of nitrated or acetylated sample was compared with the activity of the unmodified enzyme, practically no change was found in catalytic activity on casein or on N-benzoyl-L-arginine ethyl ester used as the substrate.
