| X-RAY DIFFRACTION |
? |
? |
THE CRYSTALS WERE GROWN IN THE PRESENCE OF 2MM EXCESS
5'-DEOXYADENOSYLCOBALAMIN (COENZYME B12) AND 12MM
DESULPHO-COA (FINAL CONCENTRATIONS), EQUILIBRATED
AGAINST 14% W/V PEG 4000 AND 20% V/V GLYCEROL, 100MM
TRIS PH 7.5. THE ELECTRON DENSITY MAPS SHOW NO ADENOSYL
GROUP ATTACHED TO THE COBALT ATOM, AND SPECTRA FROM
SIMILAR CRYSTALS SHOW EVIDENCE OF SUBSTANTIAL REDUCTION
OF COIII TO COII, WHICH IS 5-COORDINATE. THE COBALAMIN
IN THIS CRYSTAL STRUCTURE IS BEST CONSIDERED AS REDUCED
COB(II)ALAMIN (OR B12R). THE BOND LENGTH FROM THE COBALT
TO THE LOWER AXIAL LIGAND, NE2 OF HIS A 610 (OR HIS C 610)
IS SIGNIFICANTLY LONGER THAN THAT IN MODEL COMPOUNDS.
POORLY ORDERED LOOPS: DENSITY IN THE FOLLOWING REGIONS
IS POOR, AND THE MODEL MUST BE CONSIDERED UNRELIABLE.
ALPHA CHAIN: A 1, C 1 MISSING, A 2 - A 3, C 2 - C 3 WEAK.
BETA CHAIN: B 1 - C 19, C 1 - C 16 MISSING; B 184 - B 191,
D 184 - D 191 WEAK; D 228 - D 230 WEAK; D 271 - D 276
VERY POOR DENSITY (MUCH BETTER IN CHAIN B); D 315 WEAK;
D 474 - D 428 WEAK. |
