We study, by laser flash photolysis, the effects of ionic strength on the kinetics of the reaction 3Zncyt + az(II)-->Zncyt+ + az(I), i.e., oxidative quenching of the triplet state of zinc cytochrome c by the wild-type form and the following three mutants of cupriazurin: Met44Lys, Met64Glu, and the double mutant Met44Lys/Met64Glu. Mutations in the hydrophobic patch of azurin significantly affect the reactivity of the protein with the triplet state of zinc cytochrome c. Dependence on the ionic strength of the bimolecular rate constant for the aforementioned reaction is analyzed by several electrostatic models. The two transition-state theories, Brønsted-Debye-Hückel and van Leeuwen theories, allow the best approximation to the experimental data when effective charges of the proteins are used. Protein-protein interactions are also analyzed in terms of local charges on the protein surfaces. The rate constants depend little on ionic strength, and the monopolar and dipolar electrostatic interactions between zinc cytochrome c and azurin are not well resolved. Semiquantitative analysis of electrostatic interactions indicates that azurin uses its hydrophobic patch for contact with zinc cytochrome c.

SummaryAn approach to computer synthesis and retrosynthesis of organic compounds was formulated, and the CASB (Computer-Assisted Structure Building) software for its computer implementation was created. The approach was evaluated by the example of computer generation of probable routes for reactions of homolytic decomposition. Elementary steps of homolysis reactions were modeled with the use of the``retrosynthetic'' method. Each elementary reaction describes fragments that should be present in the structure and structural modi®cations that should be carried out to obtain reaction products. Target fragments are described in terms of production rules by specifying types of atoms, their formal charges and radical states, numbers of adjacent heteroatoms, hybridizations, etc. All possible intermediates of molecular homolysis reactions are generated by the program in a single step and then used in further search for probable pathways of decomposition during subsequent steps until the given maximum number of steps is achieved. Screening of advantageous pathways for these reactions was based on a set of empirical rules. The results obtained by the suggested approach and the corresponding program were illustrated by the example of some cyclic nitramines (RDX and HMX) and demonstrated good agreement with the experiment.

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