VISUALIZATION OF A PERIPHERAL STALK IN V-TYPE ATPASE - EVIDENCE FOR THE STATOR STRUCTURE ESSENTIAL TO ROTATIONAL CATALYSIS

F- and V-type ATPases are central enzymes in energy metabolism that co uple synthesis or hydrolysis of ATP to the translocation of H+ or Naacross biological membranes. They consist of a soluble headpiece that contains the catalytic sites and an integral membrane-bound part that conducts the ion flow. Energy coupling is thought to occur through the physical rotation of a stalk that connects the two parts of the enzym e complex. This mechanism implies that a stator-like structure prevent s the rotation of the headpiece relative to the membrane-bound part. S uch a structure has not been observed to date. Here, we report the pro jected structure of the V-type Na+-ATPase of Clostridium fervidus as d etermined by electron microscopy. Besides the central stalk, a second stalk of 130 Angstrom in length is observed that connects the headpiec e and membrane-bound part in the periphery of the complex. This additi onal stalk is likely to be the stator.