Department of Biological Sciences Purdue University, West Lafayette Ind. 47907, U.S.A.;Department of Biological Sciences Northwestern University, Evanston Ill. 60201, U.S.A.
Abstract:
The orientation of the molecular 2-fold axes of mouse testicular lactate dehydrogenase (LDHase3-C4) was determined by a rotation function search. These were subsequently identified with the P, Q, and R axes of dogfish LDHase-M4. Since LDHase-C4 crystallized with one molecule in a triclinic cell, the origin of the co-ordinate system was arbitrarily fixed at the molecular center. Structure factor phases were derived from an appropriately oriented dogfish apo LDHase-M4 phasing model and combined with the observed structure amplitudes to produce a hybrid electron density map. Density points related by the molecular 222 point symmetry were averaged so as to remove the bias of the phasing model. At 7.5 Å resolution, the structure of the crystallized mouse LDHase-C4 was found to be without coenzyme, with a conformation indistinguishable from that of dogfish apo LDHase-M4.