Comparison of solution and crystal properties of Co(II)-substituted human carbonic anhydrase II.
Arch Biochem Biophys
; 502(1): 53-9, 2010 Oct 01.
Article
en En
| MEDLINE
| ID: mdl-20637176
The visible absorption of crystals of Co(II)-substituted human carbonic anhydrase II (Co(II)-HCA II) were measured over a pH range of 6.0-11.0 giving an estimate of pK(a) 8.4 for the ionization of the metal-bound water in the crystal. This is higher by about 1.2 pK(a) units than the pK(a) near 7.2 for Co(II)-CA II in solution. This effect is attributed to a nonspecific ionic strength effect of 1.4M citrate in the precipitant solution used in the crystal growth. A pK(a) of 8.3 for the aqueous ligand of the cobalt was measured for Co(II)-HCA II in solution containing 0.8M citrate. Citrate is not an inhibitor of the catalytic activity of Co(II)-HCA II and was not observed in crystal structures. The X-ray structures at 1.5-1.6A resolution of Co(II)-HCA II were determined for crystals prepared at pH 6.0, 8.5 and 11.0 and revealed no conformational changes of amino-acid side chains as a result of the use of citrate. However, the studies of Co(II)-HCA II did reveal a change in metal coordination from tetrahedral at pH 11 to a coordination consistent with a mixed population of both tetrahedral and penta-coordinate at pH 8.5 to an octahedral geometry characteristic of the oxidized enzyme Co(III)-HCA II at pH 6.0.
Texto completo:
1
Colección:
01-internacional
Base de datos:
MEDLINE
Asunto principal:
Anhidrasa Carbónica II
Tipo de estudio:
Prognostic_studies
Límite:
Humans
Idioma:
En
Revista:
Arch Biochem Biophys
Año:
2010
Tipo del documento:
Article
País de afiliación:
Estados Unidos
Pais de publicación:
Estados Unidos