CHAPTER 4
 DEVELOPMENT OF CYSTEINE CHEMICAL MODIFICATIONS OF ALTERED b
 SUB UNITS

 Introduction

 F1Fo ATP synthases utilize the electrochemical gradient of protons across

membranes to synthesize ATP from ADP and Pi (3, 290, 291). In E. coli, F1Fo ATP

synthase is a multimeric enzyme composed of twenty-two polypeptides of eight different

types (Figure 4-1). The Fl portion is composed of the subunits a3 3Y6s and is

responsible for catalysis. The Fo portion of the enzyme consists of the ab2C10 Subunits

and conducts proton translocation through the membrane. Two stalk structures link the

Fl and Fo sectors. Proton translocation drives the rotation of the central stalk, known as

the "rotor", within the stationary u3 3 hexamer, resulting in conformational changes

within the catalytic sites (3, 15, 16, 63, 64). A second stalk structure, known as the

peripheral stalk, consists of the 6 and b subunits (Figure 4-1). The role of the peripheral

stalk is thought to be that of a "stator", holding the hexamer in place against the rotation

of the central stalk. The 6 subunit can be chemically fixed to a single a subunit without

loss of enzyme activity, which would be expected if 6 was part of the peripheral stalk

linking Fl and Fo, supporting the "stator" concept (185). The carboxyl termini of the 6

and b subunits have been shown to be in direct contact (3, 142, 200, 219, 220).