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  • Structural and electronic factors in heterolytic cleavage: formation of the Co(I) intermediate in the corrinoid/iron-sulfur protein from Clostridium thermoaceticum.

Structural and electronic factors in heterolytic cleavage: formation of the Co(I) intermediate in the corrinoid/iron-sulfur protein from Clostridium thermoaceticum.

Biochemistry (1995-04-18)
M D Wirt, M Kumar, J J Wu, E M Scheuring, S W Ragsdale, M R Chance
ABSTRACT

We have completed the first direct structural characterization of an enzyme-bound four-coordinate Co(I) intermediate, in this case for the corrinoid/iron-sulfur protein (C/Fe-SP) from Clostridium thermoaceticum. Extended X-ray absorption fine structure and X-ray edge spectroscopy of the active Co(I) state of the C/Fe-SP indicates a four-coordinate (distorted) square-planar structure where the best fit gives average Co-N(equatorial) distances of 1.87 +/- 0.01 A, corresponding to 4.2 +/- 0.3 ligands. The X-ray edge spectrum of Co(I) C/Fe-SP contains a moderate intensity 1s-4p + "shake-down" (SD) transition and no 1s-3d peak (where SD transitions are indicative of square-planar geometries). X-ray edge results for the methyl-Co(III) form, reported earlier [Wirt, M. D., Kumar, M., Ragsdale, S. W., & Chance, M. R. (1993) J. Am. Chem. Soc. 115, 2146-2150], are consistent with a base-off methylcobamide structure. The absence of a ligated 5-methoxybenzimidazole base in the methyl-Co(III) state is important since the base-off form is predicted to predispose the Co-C bond toward heterolytic cleavage to form the four-coordinate Co(I) species concurrent with methyl transfer. Additionally, we have examined first-derivative X-ray edge spectra of Co(I) C/Fe-SP, relative to edge spectra of a cobalt foil, as an indicator of effective nuclear charge on cobalt. The Co(I) C/Fe-SP edge position at 7720.5 +/- 0.3 eV is less than, but very close to, the value seen for the corresponding free Co(I) cobalamin.(ABSTRACT TRUNCATED AT 250 WORDS)

MATERIALS
Product Number
Brand
Product Description

Cobalt, foil, not light tested, 100x100mm, thickness 0.05mm, as rolled, 99.99+%
Cobalt, foil, not light tested, 100x100mm, thickness 0.01mm, 99.9%
Cobalt, foil, not light tested, 150x150mm, thickness 0.015mm, 99.9%
Cobalt, foil, light tested, 50x50mm, thickness 0.009mm, 99.9%
Cobalt, foil, not light tested, 100x100mm, thickness 0.008mm, 99.9%
Cobalt, foil, not light tested, 100x100mm, thickness 0.007mm, 99.9%
Cobalt, foil, 6mm disks, thickness 0.008mm, 99.9%
Cobalt, foil, 4mm disks, thickness 0.015mm, 99.9%
Cobalt, foil, 8mm disks, thickness 0.003mm, 99.9%
Cobalt, foil, 25mm disks, thickness 0.25mm, as rolled, 99.99+%
Cobalt, foil, 6mm disks, thickness 0.009mm, 99.9%
Cobalt, foil, 4mm disks, thickness 0.01mm, 99.9%
Cobalt, foil, 6mm disks, thickness 0.25mm, as rolled, 99.9%
Cobalt, foil, 4mm disks, thickness 0.25mm, as rolled, 99.99+%
Cobalt, foil, 4mm disks, thickness 0.003mm, 99.9%
Cobalt, foil, 6mm disks, thickness 0.02mm, 99.9%
Cobalt, foil, 4mm disks, thickness 0.125mm, as rolled, 99.99+%
Cobalt, foil, light tested, 100x100mm, thickness 0.05mm, as rolled, 99.99+%
Cobalt, foil, 8mm disks, thickness 0.006mm, 99.9%
Cobalt, foil, 6mm disks, thickness 0.005mm, 99.9%
Cobalt, foil, 6mm disks, thickness 0.01mm, 99.9%
Cobalt, foil, 6mm disks, thickness 0.0125mm, 99.9%
Cobalt, foil, 4mm disks, thickness 0.25mm, as rolled, 99.9%
Cobalt, foil, 6mm disks, thickness 0.25mm, as rolled, 99.99+%
Cobalt, foil, 4mm disks, thickness 0.004mm, 99.9%
Cobalt, foil, 8mm disks, thickness 0.01mm, 99.9%
Cobalt, foil, 6mm disks, thickness 0.015mm, 99.9%
Cobalt, foil, 4mm disks, thickness 0.02mm, 99.9%
Cobalt, foil, 6mm disks, thickness 0.025mm, 99.9%
Cobalt, foil, 50mm disks, thickness 0.125mm, annealed, 99.9%