Oxygen-bindingproteins
Hemoglobin is one of the two oxygen-binding proteins found in vertebrates. The basic function of hemoglobin is to carry O2 in blood from the lungs to other tissues in body, in order to supply the cells with the O2 required by them for oxidative phosphorylation of foodstuffs. The hemoglobin is found in blood within erythrocytes (red blood cells). These cells essentially act, between other things, as a sack for carrying hemoglobin, as mature erythrocytes lack any internal organelles (such as nucleus, mitochondria, etc.). The other O2-binding protein is myoglobin, which stores oxygen in tissues of body ready for when the cells require it. The maximum concentrations of myoglobin are found in skeletal and the cardiac muscle which require large amounts of O2 due to their need for large amounts of energy during contration.