[The hemoglobin molecule from a cybernetic and thermodynamic point of view (author's transl)]

The biological macromolecule hemoglobin (Hb) represents a reversibly functioning molecular machine. The Hb molecule is engaged in inner or structural work, which is cyclic in nature and is regulated through an exchange with the external milieu, of warmth and matter. The endothermic process of deoxygenation requires an external milieu that gives off warmth and that absorbs oxygen; the exothermic process of oxygenation, on the other hand, requires an external milieu that absorbs warmth and gives up oxygen. The Hb molecule exists in two extreme states: in a signal state for oxygenation and in a target state for deoxygenation. The transition from the signal to the target state occurs via the information process that is coupled to the structural work of the Hb molecule, whereby the absorbed warmth is converted via the structural work, without loss of energy, into the structural energy of the Hb molecule.