Structure and Function of Hemoglobin: The Cooperative Mechanism

Hemoglobin, because of its vital role in oxygen transport and its status as a model for cooperative proteins, has been the subject of a wide range of physical and chemical studies for many years. This chapter presents a brief introduction to the thermodynamic and structural aspects of cooperativity in hemoglobin. It outlines a detailed statistical mechanical model for cooperativity. The chapter also outlines the structural results and complementary theoretical studies that provide information on the origin of the structural changes that occur in ligand binding and their energetic correlates. A chemical approach to hemoglobin must provide an explanation of cooperativity in terms of specific electronic and atomic interactions and their structural and energetic consequences. From the structural and related studies, it is evident that normal human adult hemoglobin is a tetramer composed of four chains that are identical in pairs, both in terms of amino acid sequence and structure.