name,one_letter_code,three_letter_code,monoisotopic_mass,average_mass
asparagine or aspartic acid,B,ASX,114.5349352675,114.59502
glutamine or glutamic acid,Z,GLX,128.5505853375,128.6216
isoleucine or leucine,J,XLE,113.084064015,113.1594
unknown,X,XAA,0.0,0.0