title: Kinetic study of catalytic CO(2) hydration by water-soluble model compound of carbonic anhydrase and anion inhibition effect on CO(2) hydration.
abstract: A kinetic study of CO(2) hydration was carried out using the water-soluble zinc model complex with water-soluble nitrilotris(2-benzimidazolylmethyl-6-sulfonate) L1S, [L1SZn(OH(2))](-), mimicking the active site of carbonic anhydrase, in the presence and absence of anion inhibitors NCS(-) and Cl(-). The obtained rate constants k(cat) for CO(2) hydration were 5.9x10(2), 1. 7x10(3), and 3.1x10(3) M(-1) s(-1) at 5, 10, and 15 degrees C, respectively: the k(cat)=ca. 10(4) M(-1) s(-1) extrapolated towards 25 degrees C has been the largest among the reported k(cat) using zinc model complexes for carbonic anhydrase. It was also revealed that NCS(-), Cl(-) and acetazolamide play a role of inhibitors by the decrease of k(cat): 7x10(2) and 2x10(3) M(-1) s(-1) for NCS(-) and Cl(-) at 15 degrees C, respectively. The sequence of their magnitudes in k(cat) is Cl(-) approximately acetazolamide>NCS(-), where the sequence Cl(-)>NCS(-) is confirmed for native carbonic anhydrase. The difference of k(cat) or k(obs) between NCS(-) and Cl(-) resulted from that between the stability constants K(st)=2x10(3) for [L1SZn(NCS)](2-) and 1x10(2) M(-1) for [L1SZnCl](2-) in D(2)O: for water-insoluble tris(2-benzimidazolylmethyl)amine L1, K(st)=1.8x10(4) for [L1Zn(NCS)](2-) and 1.5x10(3) M(-1) for [L1ZnCl](2-)in CD(3)CN/D(2)O (50% v/v). The crystal structure of anion-binding zinc model complexes [L1Zn(OH(2))](0.5)[L1ZnCl](0.5) (ClO(4))(1.5) 1(0.5)2(0.5)(ClO(4))(1.5) was revealed by X-ray crystallography. The geometry around Zn(2+) in 1 and 2 was tetrahedrally coordinated by three benzimidazolyl nitrogen atoms and one oxygen atom of H(2)O, or Cl(-).
authors.affiliation: Division of Material Science, Graduate School of Environmental Earth Science, Hokkaido University, Sapporo 060-0810, Japan.
authors.forename: Kou
authors.initials: K
authors.lastname: Nakata
authors.forename: Noriyuki
authors.initials: N
authors.lastname: Shimomura
authors.forename: Naomi
authors.initials: N
authors.lastname: Shiina
authors.forename: Mitunori
authors.initials: M
authors.lastname: Izumi
authors.forename: Kazuhiko
authors.initials: K
authors.lastname: Ichikawa
authors.forename: Motoo
authors.initials: M
authors.lastname: Shiro
mesh_terms: D000838:Anions / Q000494:pharmacology; D001562:Benzimidazoles / Q000737:chemistry* / Q000378:metabolism*; D001665:Binding Sites; D002245:Carbon Dioxide / Q000378:metabolism*; D002256:Carbonic Anhydrases / Q000737:chemistry* / Q000378:metabolism*; D002384:Catalysis; D018360:Crystallography, X-Ray; D006863:Hydrogen-Ion Concentration; D057927:Hydrophobic and Hydrophilic Interactions; D007700:Kinetics; D008958:Models, Molecular; D018716:Molecular Mimicry; D015394:Molecular Structure; D009570:Nitriles / Q000737:chemistry* / Q000378:metabolism*; D012995:Solubility; D013696:Temperature; D014867:Water / Q000378:metabolism*; D015032:Zinc / Q000378:metabolism
chemical_list: D000838:Anions; D001562:Benzimidazoles; D009570:Nitriles; C460961:nitrilotris(2-benzimidazolylmethyl-6-sulfonate); D014867:Water; D002245:Carbon Dioxide; D002256:Carbonic Anhydrases; D015032:Zinc