Rotor A ATP Synthase John Walker The molecule Adenosine Tri Phosphate (ATP) is the source of energy in our bodies. When our muscles flex it is converted into Adenosine Di Phosphate and Phosphate ATPADP + P ADP + P ATP The electric motor enzyme ATP synthase converts ADP back to ATP You make almost your bodyweight of ATP every day During the oxy- to deoxy- transition, several hydrogen bonds and salt bridges are formed, as significant conformational changes occur in the (and identical ) interface. Selected residues which are in contact in either the oxy or deoxy conformation of Hb are illustrated in the following animation. Here the structures have been superimposed at the "flexible joint" region, where the FG segment and G helix of the chain contact the C helix of the chain. Inter-subunit contacts in this region ( and 36-40) remain relatively unchanged during the change in ligation state interface Rotor A ATP Synthase John Walker ATP Synthase the electric motor inside our bodies John Walker This animation shows residues within 8 of the two-fold axis of Hb, and illustrates the enlargement of the central cavity which occurs upon deoxygenation. Note the motion of the C-terminal Histidines of and, towards the upper and lower edges of the figure, respectively. The C-terminal Arginines of the subunits also move apart dramatically, towards the upper left and lower right corners; in front of the subunits in the figure. The ligand (2,3)-BPG binds to positively-charged residues in the subunits, in the vicinity of the central cavity. While this ligand is too bulky to fit into the narrow cavity of oxy-Hb, it binds readily in the larger cavity of the deoxy conformation. Thus, (2,3)-BPG lowers the oxygen affinity of Hb by shifting the equilibirium of the protein towards its deoxy state. Hb central cavity Then hole in the center of ATP Synthase