A low-resolution study of testicular lactate dehydrogenase using the molecular replacement technique

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.     

Carbon-13 nuclear magnetic resonance spectroscopy of high-spin iron(III) prophyrin compounds

¹³C nuclear magnetic resonance spectra have been obtained for variety of high-spin iron(III) porphyrin compounds and corresponding μ-oxo-bridged dimeric species. Large hyperfine shifts and significant line broadening are observed. The monomeric exhibit hyperfine shifts which are downfield with te exception of an upfield shift for the meso-carbon atom. Possible unpaired spin delocalization mechanisms and prospects for observing ¹³C NMR porphyrin resonances in high-spin ferrihemoproteins are discussed. Spectra reported here provide strategy for incorporation of ¹³C labels in hemoproteins either by biosynthetic or chemical means. The vinyl-CH₂ resonances of iron(III) protoporphyrin IX located 260 parts per million downfield from tetramethylsilane are especially attractive from the standpoint of chemical labeling.