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The properties of the atoms and bonds in the set of substituted benzenes Ph-X, with X = O", NH2, OH, F, CH3, H, CN, N02, NH3+, at 6-31G**/6-31G are investigated by using the theory of atoms in molecules. The directing ability of a substituent and its ability to activate or deactivate the phenyl group in electrophilic aromatic substitution reactions are shown to be a consequence of the properties of the charge distributions of the reactant molecules. These abilities are not reflected in the total charges of the phenyl group or of its individual atoms. They are reflected in the ir populations and quadrupole moments of the ring carbon atoms and in the ellipticities of the C-H bonds of the phenyl group. It is shown that the Laplacian of the total charge distribution of the reactant molecule, together with the net charge on the ipso carbon atom, can be used to predict the sites of electrophilic attack and their relative susceptibility to such attack, as well as the direction of approach of the electrophile and the relative activating-deactivating ability for each substituent.

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The crystal structure of the microbial transglutaminase (MTGase) zymogen from Streptomyces mobaraense has been determined at 1.9-Å resolution using the molecular replacement method based on the crystal structure of the mature MTGase. The overall structure of this zymogen is similar to that of the mature form, consisting of a single disk-like domain with a deep active cleft at the edge of the molecule.

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