| Popis: |
The effect of redox-inactive cationic and anionic paramagnetic chromium(III) complexes on the H-1 NMR spectrum of the reduced type 1 blue copper protein amicyanin, AmCu1, from Thiobacillus versutus has been studied as a means of defining sites for association at the protein surface. With [Cr(CN)(6)](3-) two sites are detected, one at the adjacent hydrophobic patch close to the exposed imidazole of the co-ordinated His-96, and the other at Phe-92 which has Lys-59, Lys-60, Arg-69 and Arg-100 in close proximity and is adjacent to the active site-co-ordinated Cys-93. In contrast, the cationic complexes [Cr(NH3)(6)](3+) and [Cr(en)(3)](3+) (en = ethane-2,2-diamine) cause no significant line broadening and no preferred sites for association are detected. Kinetic stopped-flow studies on the competitive inhibition by [Cr(CN)(6)](3-) of the [Fe(CN)(6)](3-) oxidation of AmCu1 indicate that [Fe(CN)(6)](3-) reacts at two sites, one of which is inhibited by [Cr(CN)(6)](3-) and the other is unaffected by [Cr(CN)(6)](3-). It is suggested that the first of these corresponds to reaction at the Phe-92 site, contributing 25% to the reaction, and the second to reaction at His-96. Therefore, in its reaction with [Fe(CN)(6)](3-) amicyanin has adjacent and remote binding sites. |
