[mrlucky0]

According to my biochemistry text:

Acid Hydrolysis of Proteins

" Peptide bonds of proteins are hydrolyzed by either strong acid or strong base. Because acid hydrolysis proceeds without racemization and with less destruction of certain amino acids (Ser, Thr, Arg, and Cys) than alkaline treatment, it is the method of choice in analysis of the amino acid composition of proteins and polypeptides. Typically, samples of a protein are hydrolyzed with 6 N HCl at 110°C for 24, 48, and 72 hr in sealed glass vials. Tryptophan is destroyed by acid and must be estimated by other means to determine its contribution to the total amino acid composition. The OH-containing amino acids serine and threonine are slowly destroyed, but the data obtained for the three time points (24, 48, and 72 hr) allow extrapolation to zero time to estimate the original Ser and Thr content (Figure). "

I thought about it over and over but I cannot understand why Tryptophan is destroyed by strong acid. The indole N does not behave like a base because its lone pair stabilizes the Pi system.

My reasoning should be right, but maybe I am misinterpreting the text? Can anyone clarify?

[Arkcon]

The addition of phenol to the hydrolysis vessel protects all of the amino acids from oxidation.  Once, I put much more than was required by the procedure, and tryptophan survived the hydrolysis.  This leads me to believe that it is more sensitive to oxidation, even by trace amounts of O₂, under acid hydrolysis conditions.

Lookie here, lots of people are aware of this, these days:
{Google search}

[mrlucky0]

Hey. Thanks.