But in aspital protease, the residues don't actually act as nuclear files. Instead it's the water that will ultimately act as the nuclear file. Now the similarity between, let's say cysteine protease and aspirin protease is we still have to transform the water into a good nuclear file in the same way that we had to transform the cysteine into a strong nuclear file before the nuclearphilic attack took place. In this particular case we see that we're going to have residues that will transform the water into a better nuclear phile. Now if we examine the active side of aspir proteases we're going to find two residues. One of these residues will be aspartic acid and the other one will be aspartate.