Quaternary Structure (4^o Structure).

• Globular in structure.
• When two or more than two molecules of protein of tertiary structure are connected to each other through various bonds then this structure is called quaternary structure.
• Most stable protein.
• Haemoglobin has 4 polypeptide chains (2 a chains & 2 b chains).
• Insulin consists of 2 polypeptide chains (1 a chain & 1 b chain).
• A chain of insulin consists of 21 amino acids and b chain insulin consists 30 amino acids.
• Total numbers of 51 amino acids are present in insulin
• Molecular structure of insulin described by F. Sanger (He got 1st time Nobel Prize)
• He got 2nd time Nobel Prize for preparing chromosomal maps.

• Quaternary structure was first studied in case of haemoglobin by Kendrew and Perutz (1963).