Recovery of tryptophan in peptides and proteins by high-temperature and short-term acid hydrolysis in the presence of phenol

The addition of 3% ( w v) phenol to 6 M HCl largely prevented the destruction of tryptophan during rapid hydrolysis of peptides and proteins at 166°C for 25 min or at 145°C for 4 h. This hydrolysis procedure was advantageous for amino acid microanalysis using conventional high-performance liquid chromatography with a precolumn derivatization technique. The recovery of tryptophan from proteins was at least 80%. The addition of phenol also improved the recovery of methionine and carboxymethylcysteine. The amount of tryptophan in proteins electroblotted onto a polyvinylidene difluoride membrane was determined by this method.