Hemoglobin, an Allosteric Protein

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  • 9.1 Hemoglobin Displays Cooperative Behavior

  • 9.2 Myoglobin and Hemoglobin Bind Oxygen in Heme Groups

  • 9.3 Hemoglobin Binds Oxygen Cooperatively

  • 9.4 An Allosteric Regulator Determines the Oxygen Affinity of Hemoglobin

  • 9.5 Hydrogen Ions and Carbon Dioxide Promote the Release of Oxygen

  • 9.6 Mutations in Genes Encoding Hemoglobin Subunits Can Result in Disease

In the bloodstream, red blood cells carry oxygen from the lungs to tissues where oxygen is required. Hemoglobin, a four-subunit protein with an oxygen-binding pigment called heme, which gives blood its color, transports oxygen and releases it where it is needed.

A fascinating protein called hemoglobin is a component of red blood cells. This protein efficiently carries oxygen from the lungs to the tissues and contributes to the transport of carbon dioxide and hydrogen ions back to the lungs.

Hemoglobin is a wonderful example of the fact that allostery is not a property limited to enzymes. The basic principles of allostery are well illustrated by hemoglobin. Indeed, many of the principles of allosteric regulation were elucidated by the study of hemoglobin, the first allosteric protein known in atomic detail. The study of allosteric enzymes and hemoglobin is so intertwined that hemoglobin was designated an “honorary enzyme” by biochemist Jacques Monod.

In this chapter, we will examine the allosteric properties of hemoglobin, including how the oxygen-carrying capacity of this protein is regulated to meet the physiological requirements of an organism. We will also look at a close chemical relative of hemoglobin, the protein myoglobin. Located in muscle, myoglobin facilitates the diffusion of the oxygen to cellular sites that require oxygen and provides a reserve supply of oxygen in times of need.

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