J. Phys. IV France 04 (1994) C9-303-C9-307
The influence of the effectors of yeast pyruvate decarboxylase (PDC) on the conformation of the dimers and tetramers and their pH-dependent equilibriumS. König1, D. Svergun2, M.H.J. Koch2, G. Hübner1 and A. Schellenberger1
1 Institute of Biochemistry, Department of Enzymology, Martin-Luther-University Halle-Wittenberg, Weinbergweg 16a, 06099 Halle, Germany
2 European Molecular Biology Laboratory, Hamburg Outstation, EMBL c/o DESY, Notkestr. 85, 22603 Hamburg, Germany
The influence of effectors of yeast pyruvate decarboxylase, phosphate, pyruvamide, thiamin diphosphate and Mg++, on the pH-dependent equilibrium between dimers and tetramers was studied by synchrotron radiation X-ray solution scattering. Thiamin diphosphate and phosphate shift the equilibrium to higher values without altering the structure of the oligomers. Pyruvamide, a substrate analogue activator, induces a significant change in the structure of the tetramer. By eliminating radiation damage by addition of dithioerythrol to the buffers, the scattering curves could be measured accurately over a large angular range. They were expanded in terms of spherical harmonics to obtain the shapes of the dimers and tetramers with higher resolution than was hitherto possible. This also allowed us to position the dimers, which are centrosymmetric at low resolution, in the tetramers which have 222 symmetry. The results indicate that addition of pyruvamide results in a less compact tetramer owing to structural changes in the dimers and to their displacements.
© EDP Sciences 1994