Question 28.2: Determining the Sequence of Amino Acids in a Polypeptide A p...
Determining the Sequence of Amino Acids in a Polypeptide
A polypeptide, on complete hydrolysis, yielded the amino acids A, B, C, D, and E. Partial hydrolysis and sequence proof gave single amino acids, together with the following larger fragments: AD, CD, DCB, BE, and BC. What must be the sequence of amino acids in the polypeptide?
Analyze
Begin by arranging the fragments in the following manner,
\begin{matrix} \text{AD} \\ \ \ \ \ \ \text{ DC} \\ \ \ \ \ \ \ \ \ \ \text{DCB} \\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{ BE} \\ \ \ \ \ \ \ \ \ \ \ \ \ \text{ CB} \end{matrix}
We see that the sequence ADCBE is consistent with the fragments observed.
Assess
Typically, we write a sequence starting from the N-terminal amino acid and ending at the C-terminal amino acid. Therefore, the sequence EBCDA is also possible because we do not know whether A or E is the N-terminal end of the polypeptide.