Chapter 5, Problem 33CQ

Summary Introduction

To determine: The position of disulfide bonds in the intact polypeptide.

Concept introduction: Proteins are made up of one or more amino acids linked together to form a chain. The building blocks of the protein is called amino acid. Amino acids are termed as residues if they release a hydrogen ion from the amine end or a hydroxyl ion from the carboxyl end, or both; a water molecule is released as a result of formation of each amide bond. When more than eight peptides are linked together by peptide bonds, it forms a polypeptide.

Given:

• Treatment of a polypeptide with 2-mercaptoethanol yields two polypeptides: Ala-Val-Cys-Arg-Thr-Gly-Cys-Lys-Asn-Phe-Leu, Tyr-Lys-Cys-Phe-Arg-His-Thr-Lys-Cys-Ser.
• Treatment of the intact polypeptide with trypsin yields seven peptide fragments: Ala, Arg, Cys₂, Ser, Val; Arg, Cys₂, Gly, Lys, Thr, Phe; Asn, Leu, Phe; His, Lys, Thr; Lys, Tyr.