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Myoglobin is an iron- and oxygen-binding protein found in the muscle tissue of vertebrates in general and in almost all mammals. It is related to hemoglobin, which is the iron- and oxygen-binding protein in blood, specifically in the red blood cells. In humans, myoglobin is only found in the bloodstream after muscle injury. It is an abnormal finding, and can be diagnostically relevant when found in blood. 〔 (Google books link is the 2008 edition)〕 Myoglobin is the primary oxygen-carrying pigment of muscle tissues. High concentrations of myoglobin in muscle cells allow organisms to hold their breath for a longer period of time. Diving mammals such as whales and seals have muscles with particularly high abundance of myoglobin.〔 Myoglobin is found in Type I muscle, Type II A and Type II B, but most texts consider myoglobin not to be found in smooth muscle. Myoglobin was the first protein to have its three-dimensional structure revealed by X-ray crystallography.〔((U.S.) National Science Foundation: Protein Data Bank Chronology (Jan. 21, 2004) ). Retrieved 3.17.2010〕 This achievement was reported in 1958 by John Kendrew and associates. For this discovery, John Kendrew shared the 1962 Nobel Prize in chemistry with Max Perutz.〔(The Nobel Prize in Chemistry 1962 )〕 Despite being one of the most studied proteins in biology, its physiological function is not yet conclusively established: mice genetically engineered to lack myoglobin are viable, but showed a 30% reduction in volume of blood being pumped by the heart during a contraction. They adapted to this deficiency through natural reactions to inadequate oxygen supply (hypoxia) and a widening of blood vessels (vasodilation). In humans myoglobin is encoded by the ''MB'' gene. ==Differences from Hemoglobin== Myoglobin is similar to hemoglobin in that it is involved in the transportation of oxygen to cells. There are many distinct differences that set the protein apart from hemoglobin. For one the protein has only one binding site for oxygen on the one heme group on the protein. While myoglobin can only hold one oxygen, the affinity for that oxygen is very high compared to hemoglobin. This is likely due to the fact that hemoglobin, transporting 4 oxygens to the tissues and muscles where myoglobin is mostly present. The myoglobin takes the oxygen from the hemoglobin (due to the Bohr Effect) and takes that oxygen to muscle cells for use in metabolic processes. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「myoglobin」の詳細全文を読む スポンサード リンク
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