In order to obtain the evolutionary distance data that are as purely additive as possible, we have developed a novel method for evaluating the evolutionary distances from the base-pair changes in stem regions of ribosomal RNAs (rRNAs). The application of this method to small-subunit (SSU) and large-subunit (LSU) rRNAs provides the distance data, with which both the unweighted pair group method of analysis and the neighbor-joining method give almost the same tree topology of most organisms except for some Protoctista, thermophilic bacteria, parasitic organisms, and endosymbionts. Although the evolutionary distances calculated with LSU rRNAs are somewhat longer than those with SSU rRNAs, the difference, probably due to a slight difference in functional constraint, is substantially decreased when the distances are converted into the divergence times of organisms by the measure of the time scale estimated in each type of rRNAs. The divergence times of main branches agree fairly well with the geological record of organisms, at least after the appearance of oxygen-releasing photosynthesis, although the divergence times of Eukaryota, Archaebacteria, and Eubacteria are somewhat overestimated in comparison with the geological record of Earth formation. This result is explained by considering that the mutation rate is determined by the accumulation of misrepairs for DNA damage caused by radiation and that the effect of radiation had been stronger before the oxygen molecules became abundant in the atmosphere of the Earth.
The electronic structure of ferrous heme with imidazole as the fifth ligand. II. Explanation of MCD spectra from the near IR region to the Soret region J. Chem. Phys. 72, 6059 (1980); 10.1063/1.439062
Nonempirical LCAO MO SCF and CI Studies of the Low Lying Electronic State of the HOO RadicalA semiempirica1 molecular orbital calculation is performed on the porphin-Fe-imidazole system. As basic atomic orbitals. lone pair a orbitals of the N atoms coordinating to Fe are employed in addition to 3d ortibals of Fe and 1/" orbitals of Nand C atoms. Molecular orbitals are obtained by the usual SCF procedure for the closed shell configuration. Then the calculation of the open shell states is carried out by a careful configuration interaction method. The ground state is identified with one component of sE.The energy level scheme suggested by magnetic measurements and by ligand field theory for low-lying quintet, singlet. and triplet states is well reproduced. Corresponding to a broad absorption band in the visible region and weak bands in the near JR. x -and y -polarized electronic transitions. two d-->
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