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Myoglobin is a single-chain globular protein of 153 amino acids, containing a heme (iron-containing porphyrin) prosthetic group in the center around which the remaining apoprotein folds. With a molecular weight of 16,700 daltons, it is the primary oxygen-carrying pigment of muscle tissues.[1] Unlike the blood-borne hemoglobin, to which it is structurally related,[2] this protein does not exhibit cooperative binding of oxygen, since positive cooperativity is a property reserved for multimeric proteins. Instead, the binding of oxygen by myoglobin is unaffected by the oxygen pressure in the surrounding tissue. Myoglobin is often cited as having an "instant binding tenacity" to oxygen given its hyperbolic oxygen dissociation curve. In 1958, John Kendrew and associates successfully determined the structure of myoglobin by high-resolution X-ray crystallography.[3] For this discovery, John Kendrew shared the 1962 Nobel Prize in chemistry with Max Perutz.[4]