CNBr cleavage mapping: Val-Lys-Glu-Met-Ser-Trp-Arg-Ala Cyanogen bromide (CNBr) specifically cleaves on the C-terminal side of methionine residues. What peptide fragments are produced from the sequence Val-Lys-Glu-Met-Ser-Trp-Arg-Ala?

Introduction:
Cyanogen bromide (CNBr) is a classic reagent for peptide mapping because it cleaves specifically at methionine residues, enabling predictable fragmentation for sequencing strategies.

Given Data / Assumptions:

• Sequence: Val-Lys-Glu-Met-Ser-Trp-Arg-Ala.
• CNBr cleaves at the C-terminus of Met, generating a new fragment ending with Met.
• No Met at the extreme C-terminus beyond the single internal Met.

Concept / Approach:

Identify all Met positions, then cut immediately after each Met to form fragments. The presence of only one Met means two fragments will form.

Step-by-Step Solution:

Verification / Alternative check:

Counting residues pre- and post-cleavage preserves total length (8 residues = 4 + 4), confirming consistency.

Why Other Options Are Wrong:

Other answers either split at non-Met positions or place the cut before Met, contradicting CNBr specificity.

Common Pitfalls:

Confusing CNBr (cleaves after Met) with trypsin (after Lys/Arg) or chymotrypsin (aromatics).

Final Answer:

Val-Lys-Glu-Met + Ser-Trp-Arg-Ala