Question

Which amino acid(s) can be quantified from the acid hydrolysates of proteins?

• A. Gln
• B. Gln, Asn
• C. His
• D. Gln, Asn, Trp

Hint:

Acid hydrolysis is a "destructor." It kills Trp and converts the "Amides" (Asn/Gln) to "Acids" (Asp/Glu).

Answer 1

The Correct Option is C

Step 1: Concept
Acid hydrolysis ($6\text{M HCl}$ at $110^\circ\text{C}$) is a standard method to break down proteins into their constituent amino acids for analysis.

Step 2: Analysis of Sensitivity
Certain amino acids are destroyed or converted during this process. Glutamine (Gln) and Asparagine (Asn) are deamidated to Glutamic acid and Aspartic acid. Tryptophan (Trp) is completely destroyed.

Step 3: Identification
Histidine (His) is stable under these harsh acidic conditions and can be recovered and quantified.

Step 4: Conclusion
Among the choices, only Histidine remains quantifiable. Final Answer: (C)