Humans are aerobic organisms. Our lungs extract oxygen (O2) from air and deliver carbon dioxide (CO2) in exhaled gases. The inspired O2 leads to a more efficient utilization of metabolic fuels, such as glucose and fatty acids, and expired CO2 is a major product of cellular metabolism. Living systems contain proteins that interact with O2 and, consequently, increase its solubility in water and sequester it for transport. In mammals, these proteins are myoglobin (Mb) and hemoglobin (Hb). Mb, found primarily in skeletal and striated muscle, serves to store O2 in the cytoplasm and deliver it on demand to the mitochondrion. Hb, restricted to the erythrocytes, is responsible for the transport of O2 from the lungs to peripheral tissues. This chapter presents the molecular features of heme, the biochemical and physiologic relationships between the structures of Mb and Hb and their interaction with O2, and the pathologic aspects of selected Hb mutations.
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