Characterization of cytochrome c
6 from the cyanobacterium Anabaena PCC 7119 |
| |
| Authors: | Milagros Medina Ricardo O Louro Jean Gagnon Maria Luisa Peleato Joaquim Mendes Carlos Gómez-Moreno António V Xavier M Teixeira |
| |
| Institution: | (1) Departamento de Bioquímica y Biología Molecular y Celular, Facultad de Ciencias, Universidad de Zaragoza, E-50009 Zaragoza, Spain, ES;(2) Instituto de Tecnologia Química e Biológica, Universidade Nova de Lisboa, Oeiras, APT 127, P-2780 Oeiras, Portugal, PT;(3) Institut de Biologie Structurale Jean-Pierre Ebel (CEA-CNRS), Grenoble, France, FR |
| |
| Abstract: | A soluble monoheme c–type cytochrome c
6 has been isolated from the cyanobacterium Anabaena PCC 7119. It is a basic protein, with a molecular mass of 9.7 kDa, which accepts electrons from Anabaena ferredoxin in the ferredoxin-NADP+reductase-dependent NADPH cytochrome c reductase activity assay. The turnover of the reaction has an optimum pH at 7.5. Flavodoxin can also replace ferredoxin in
this assay, but with only 20% efficiency. Plastocyanin from Anabaena PCC 7119, as well as the c
6 cytochromes from the green algae Chlorella fusca and Monoraphidium braunii are also shown to accept electrons from Anabaena ferredoxin. The reduction potential of cytochrome c
6 at pH 6.7 was determined to be 338 mV and is pH dependent, with pK
a
ox=8.4±0.1 and pK
a
red≈9.5. The ferric and ferrous cytochrome forms and their pH equilibria have been studied using visible, EPR and 1H-NMR spectroscopies. The amino acid sequence and the visible and NMR spectroscopic data indicate that the heme iron has a
methionine-histidine axial coordination in the pH range 5–11. However, the EPR data for the ferricytochrome are complex and
show that in this pH range five distinct forms are present. Between pH 5 and 9 the spectrum is dominated by two rhombic species,
with g–values at 2.94, 2.29, 1.43 and at 2.84, 2.34, 1.56, which interconvert with a pK
a of 8.4. The NMR data also show a main interconversion between two cytochrome forms at this pH, which coincides with that
determined from the pH dependence of the reduction potential. Both these forms were associated with a methionine-histidine
heme-iron coordination by correlation with the visible and NMR spectral data, although having crystal field parameters atypical
for this type of coordination. Anabaena cytochrome c
6 is one more example of a heme protein for which the widely used crystal field analysis of the EPR data (truth diagram) fails
to unequivocally determine the type of heme-iron ligation.
Received: 17 May 1996 / Accepted: 13 January 1997 |
| |
| Keywords: | Cytochrome c6 Anabaena PCC 7119 EPR NMR Redox-Bohr |
| 本文献已被 SpringerLink 等数据库收录！ |
|
