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| Content Provider | Springer Nature Link |
|---|---|
| Author | Yoo, Sun Jae Meyer, Jacques Achim, Catalina Peterson, James Hendrich, Michael P. Münck, E. |
| Copyright Year | 2000 |
| Abstract | Rubredoxins contain a mononuclear iron tetrahedrally coordinated by four cysteinyl sulfurs. We have studied the wild-type protein from Clostridium pasteurianum and two mutated forms, C9S and C42S, in the oxidized and reduced states, with Mössbauer, integer-spin EPR, and magnetic circular dichroism (MCD) spectroscopies. The Mössbauer spectra of the ferric C42S and C9S mutant forms yielded zero-field splittings, D=1.2 cm−1, that are about 40% smaller than the D-value of the wild-type protein. The 57Fe hyperfine coupling constants were found to be ca. 8% larger than those of the wild-type proteins. The present study also revealed that the ferric wild-type protein has δ=0.24±0.01 mm/s at 4.2 K rather than δ=0.32 mm/s as reported in the literature. The Mössbauer spectra of both dithionite-reduced mutant proteins revealed the presence of two ferrous forms, A and B. These forms have isomer shifts δ=0.79 mm/s at 4.2 K, consistent with tetrahedral Fe2+(Cys)3(O-R) coordination. The zero-field splittings of the two forms differ substantially; we found D=−7±1 cm−1, E/D=0.09 for form A and D=+6.2±1.3 cm−1, E/D=0.15 for form B. Form A exhibits a well-defined integer-spin EPR signal; from studies at X- and Q-band we obtained g z =2.08±0.01, which is the first measured g-value for any ferrous rubredoxin. It is known from X-ray crystallographic studies that ferric C42S rubredoxin is coordinated by a serine oxygen. We achieved 75% reduction of C42S rubredoxin by irradiating an oxidized sample at 77 K with synchrotron X-rays; the radiolytic reduction produced exclusively form A, suggesting that this form represents a serine-bound Fe2+ site. Studies in different buffers in the pH 6–9 range showed that the A:B ratios, but not the spectral parameters of A and B, are buffer dependent, but no systematic variation of the ratio of the two forms with pH was observed. The presence of glycerol (30–50% v/v) was found to favor the B form. Previous absorption and circular dichroism studies of reduced wild-type rubredoxin have suggested d-d bands at 7400, 6000, and 3700 cm−1. Our low-temperature MCD measurements place the two high-energy transitions at ca. 5900 and 6300 cm−1; a third d-d transition, if present, must occur with energy lower than 3300 cm−1. The mutant proteins have d-d transitions at slightly lower energy, namely 5730, 6100 cm−1 in form A and 5350, 6380 cm−1 in form B. |
| Starting Page | 475 |
| Ending Page | 487 |
| Page Count | 13 |
| File Format | |
| ISSN | 09498257 |
| Journal | JBIC Journal of Biological Inorganic Chemistry |
| Volume Number | 5 |
| Issue Number | 4 |
| e-ISSN | 14321327 |
| Language | English |
| Publisher | Springer-Verlag |
| Publisher Date | 2000-08-15 |
| Publisher Place | Berlin, Heidelberg |
| Access Restriction | One Nation One Subscription (ONOS) |
| Content Type | Text |
| Resource Type | Article |
| Subject | Biochemistry Inorganic Chemistry |
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