End Group Determination

Abstract

Most polypeptides and proteins occurring in nature have been shown to consist of a single polypeptide chain, but several proteins, insulin, chymotrypsin, immunoglobulin, hemoglobin and lactate dehydrogenase, for example, have been shown to be composed of more than a single chain. In protein molecules consisting of two or more polypeptide chains, the chains are held together either by covalent interpeptide-chain disulfide bonds of cystine residues (insulin, α-chymotrypsin, immunoglobulin etc.) or by the cumulative forces of ionic interaction, hydrogen bond and hydrophobic interaction between side chain groups of amino acid residues belonging to the neighboring different polypeptide chains (hemoglobin, lactate dehydrogenase etc.). Each polypeptide chain usually possesses an unsubstituted α-amino group at one end of the chain (amino terminal group or N-terminal group) and an unsubstituted α-carboxyl group at the other end (carboxyl terminal group or C-terminal group).