The peptide A on reaction with 1-fluoro-2, 4-dinitrobenzene followed by exhaustive hydrolysis gave phenylalanine, alanine, serine and $\mathrm{N}$-(2, 4-dinitrophenyl) glycine. On the other hand, pepetide A after two cycles of Edman degradation gave Phe-Ser as the product. The structure of the peptide A is
(a)Phe-Ser-Ala-Gly
(b)Phe-Ser-Gly-Ala
(c)Gly-Ala-Phe-Ser
(d)Ala-Gly-Phe-Ser
Answer
Answer: C ✓ checked by 4AB · confidence high
Explanation
Sanger's reagent labels the N-terminus: DNP-glycine, so Gly is first. Two Edman cycles remove two residues and leave Phe-Ser, so the sequence is Gly-Ala-Phe-Ser.