5.3.3.2 hanging drop vapour diffusion method, selenomethionyl form, crystals display trigonal symmetry, with unit-cell parameters, a = b = 71.3 A, c = 61.7 A, and diffract to 1.45 A resolution 649155 5.3.3.2 in complex with diphosphate. The diphosphate moiety is located near the conserved residues H10, R97, H152, Q157, E158, and W219, and the flavin cofactor. The putative active site may stabilize a carbocationic intermediate 690998 5.3.3.2 molecular modeling of structure and comparison with structures of Streptococcus pneumoniae and Thermus thermophilus enzymes 695056 5.3.3.2 native enzyme at 1.7 A and in complex with substrate at 1.9 A resolution. comparison with Escherichia coli enzyme structure 681413 5.3.3.2 of wild-type and mutants Y104A, Y104F 680660 5.3.3.2 sitting drop vapor diffusion method, ligand-free form of the FMN-bound enzyme form at 2.8 A resolution. The octamer forms a D4 symmetrical open, cage-like structure. The monomers of 45000 Da display a classical TIM barrel fold 652916 5.3.3.2 sitting drop vapor diffusion method, using 0.6 M calcium acetate and 50 mM HEPES pH 7.5 713655 5.3.3.2 sitting drop vapor diffusion method, using HEPES buffer (100 mM, pH 7.5 with 2 M (NH4)2SO4) 747530 5.3.3.2 the covalent adduct formed between irreversible mechanism based inhibitors, 3-methylene-4-penten-1-yl diphosphate or 3-oxiranyl-3-buten-1-yl diphosphate, and the flavin cofactor are investigated by X-ray crystallography and UV-visible spectroscopy. Both the crystal structures of enzyme binding the flavin-inhibitor adduct and the UV-visible spectra of the adducts indicate that the covalent bond is formed at C4a of flavin rather than at N5. The high-resolution crystal structures of enzyme-substrate complexes and the kinetic studies of new mutants confirm that only the flavin cofactor can catalyze protonation of the substrates and suggest that N5 of flavin is most likely to be involved in proton transfer 728667 5.3.3.2 the crystal structures of the substrate-free enzyme and of the substrate-enzyme complexes, in the oxidized and reduced states, are solved to resolutions between 1.99 and 3.1 A, six distinct types of type 2 IDI crystals are obtained 704638