期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：1974
卷号：71
期号：12
页码：4760-4762
DOI：10.1073/pnas.71.12.4760
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：Preparation of cobalt(II) derivatives of type 1 copper proteins has been extended to include bean plastocyanin and azurin from Pseudomonas aeruginosa. Fluorescence quenching data suggest that Co(II) binds to the type 1 site of both apoplastocyanin and apoazurin. Electronic absorption spectral measurements have been made for cobalt(II)-stellacyanin, cobalt(II)-plastocyanin, and cobalt(II)-azurin. In each case two visible bands with moderate intensities and two rather strong ultraviolet absorption peaks are observed. The intensity pattern and the separation of the two ultraviolet bands in the Co(II) derivatives correspond closely to the two intense, low-lying absorption peaks in the analogous, type 1 copper proteins. The evidence suggests that the intense, two-band systems represent ligand-to-metal charge transfer transitions in both Cu(II) and Co(II) derivatives. It is proposed that the transitions in each case originate in the 3p{pi} and 3p{sigma} orbitals of a cysteine sulfur ligand at the type 1 site. The visible absorption bands in the Co(II) derivatives are assigned to d-d transitions. The large 4P splitting observed indicates that the type 1 Co(II) site is of low symmetry. The d-d band pattern suggests that the high-spin Co(II) center is either distorted tetrahedral or five-coordinate. The observed band intensities are in much closer accord with the values for Co(II) complexes known to have distorted tetrahedral structures.
关键词：metal replacement ; electronic spectroscopy ; charge transfer transitions
