Myoglobin is a 17KDa cytoplasmic oxygen-binding protein encoded by the MB gene and expressed in myocytes of the heart and skeletal muscle. Its name derives from its structural and functional similarity to hemoglobin, the oxygen binding protein found in red blood cells. Functions of myoglobin include oxygen storage and transport, as well as scavenging of NO and reactive oxygen species. Myoglobin also serves as a sensitive marker for muscle injury resulting from cardiac infarction. Myoglobin was the first protein to have its three-dimensional structure determined by X-ray crystallography.