Myoglobin binds molecular oxygen (O2) in the cells of muscle tissue (Rossi-Fanelli and Antonini 1958, Boulton and Huntsman 1972, Wang et al. 2004). The dissociation constant of Myoglobin-oxygen is about 1 micromole per liter. The myoglobin:oxygen complex stores oxygen and also transports oxygen from the sarcolemma to the mitochondria. Myoglobin binds other small molecules such as nitric oxide and carbon monoxide. The ligands of myoglobin appear to migrate from the surface of the protein through pores (pockets) in the protein structure to reach the embedded heme group (reviewed in Tomita et al. 2010).