Absorption spectra of d10 metal ion derivatives of plastocyanin

Abstract

Near-UV absorption studies have been carried out for various metal-replaced derivatives of spinach plastocyanin. Above 250 nm plastocyanin derivatives containing Zn(II), Cd(II), or Cu(II), as well as apoplastocyanin, exhibit very similar absorptions due to phenylalanine and tyrosine residues. In contrast, forms containing Hg(II), Cu(I), or Ag(I) show enhanced absorbance in the UV region. In difference spectra with apoplastocyanin as a reference, the Hg(II) derivative exhibits a maximum around 247 nm (Ae -9800 ± 100 M'1 cm'1) and a shoulder at 280 nm (Ae = 2100 M"1 cm'1) while the Cu(I) analogue has a strong absorbance at 275 nm (Ae ^3320 ± 20 M"1 cm"1) and a weaker shoulder at 310 nm. In Ag(I) plastocyanin a band is apparent at 240 nm (Ae 5100 ± 100 M'1 cm'1). The metal dependence of the absorption spectrum suggests that the metal centers are directly involved in the transitions, and literature data support this view. For the Hg(II) derivative the bands can be assigned as S(Cys) -» Hg(II) charge-transfer absorptions analogous to transitions found in mercury thioneins. For the Cu(I) and Ag(I) derivatives the bands are plausibly assigned to metal-centered or charge-transfer transitions involving the radial extension of electron density from the zid shell. A similar assignment is advanced for bands, previously assigned as ligand-to-metal charge-transfer transitions, in the spectra of copper thioneins. These results show that UV spectra can sometimes be useful in characterizing protein derivatives containing metal ions that, on the basis of visible spectra, have been regarded as spectroscopically "silent".

Role of the active-site cysteine of Pseudomonas aeruginosa azurin. Crystal structure analysis of the CuII(Cys112Asp) protein

“…These Cu II -dependent absorption bands reappear slowly over several hours upon standing in air. Importantly, the absorption spectrum of Cu I (Cys112Asp) azurin is remarkably similar to that of the corresponding Cu I WT protein [20]; both reduced proteins show increased near-UV absorptions that can be ascribed to Cu I -centered electronic transitions [26]. In light of our finding that the copper ion is not removed by gel filtration of the [Ru II (NH 3 ) 6 ] 2c -treated Cys112Asp azurin and that the absorption spectrum of the resulting sample is very similar to that of the reduced WT protein, it is likely that Cu I remains coordinated in the Cys112Asp active site.…”

Metal-ion-center assembly of ferredoxin and plastocyanin in isolated chloroplasts.

“…Copper removal from holo-PC and other PC-related proteins was performed as described (4). In brief, proteins were reduced by adding ascorbate and the solutions were dialyzed against 25 mM Tris/HCl buffer (pH 8.0) containing 0.01 M KCN for 2 hr at 4°C to remove the Cu+.…”

“…Assembly can be achieved in vitro simply by adding copper ion to a solution containing apo-PC (4). It has been suggested that holo-PC in chloroplasts results from chelating of copper ion by apo-PC (5) rather than from an enzyme-mediated'assembly process.…”

Solution behavior of Hg(II)-cystamine by Uv-Vis and199Hg NMR

“…Hg LMCT. However, low-energy charge transfer bands for two-or three-coordinate Hg(II)-thiolates and Hg(II)-thiolates with distorted tetrahedral geometry fall in the range of 230 -250 nm and 280 -310 nm respectively [6,18,19]. Hence, the significant shift in the l max is most probably due to the close proximity of two Cl ions in the solution, which might result in equilibrium between two-and four-coordinate compound.…”