Evidence for Major Structural Changes in the Manduca sexta Midgut V sub(1) ATPase Due to Redox Modulation. A small angle X-ray scattering study

The shape and overall dimensions of the oxidized and reduced form of the V sub(1) ATPase from Manduca sexta were investigated by synchrotron radiation x-ray solution scattering. The radius of gyration of the oxidized and reduced complex differ noticeably, with dimensions of 6.20 plus or minus 0.06 and 5.84 plus or minus 0.06 nm, respectively, whereas the maximum dimensions remain constant at 22.0 plus or minus 0.1 nm. Comparison of the low resolution shapes of both forms, determined ab initio, indicates that the main structural alteration occurs in the head piece, where the major subunits A and B are located, and at the bottom of the stalk. In conjunction with the solution scattering data, decreased susceptibility to tryptic digestion and tryptophan fluorescence of the reduced V sub(1) molecule provide the first strong evidence for major structural changes in the V sub(1) ATPase because of redox modulation.