Myoglobin: an essential hemoprotein in striated muscle

Myoglobin is a cytoplasmic hemoprotein, expressed solely in cardiac myocytes and oxidative skeletal muscle fibers, that reversibly binds O-2 by its heme residue, a porphyrin ring:iron ion complex. Since the initial discovery of its structure over 40 years ago, wide-ranging work by many investigators has added importantly to our understanding of its function and regulation. Functionally, myoglobin is well accepted as an O-2-storage protein in muscle, capable of releasing O-2 during periods of hypoxia or anoxia. Myoglobin is also thought to buffer intracellular O-2 concentration when muscle activity increases and to facilitate intracellular O-2 diffusion by providing a parallel path that augments simple diffusion of dissolved O-2. The use of gene targeting and other molecular biological techniques has revealed important new insights into the developmental and environmental regulation of myoglobin and provided additional functions for this hemoprotein such as scavenging nitric oxide and reactive O-2 species. These recent findings, coupled with additional emerging technologies and the discovery of other tissue globins, provide a framework for addressing new questions about myoglobin and readdressing old ones.