Plastocyanin absorption spectrum

Figure 4. A) Room-temperature optical spectrum of a single crystal of plastocyanin obtained with light incident on the (0,1,1) face and polarized parallel (solid line) and perpendicular (dashed line) to a (from Ref. 11). B) Gaussian resolution of the 35 K visible absorption spectrum of a plastocyanin film with suggested assignments the symbols ( ) represent the experimental absorption spectrum. Right plastocyanin unit cell projected on the (0,1,1) plane, showing the positions of the four symmetry-related Cu atoms at their first coordination shells.

Figure 3. Blue copper proteins. A X-ray structure of poplar plastocyanin (21). B Absorption spectrum of plastocyanin and normal D 4 cCuCl42 (e scale expanded by 10). C X-band EPR spectrum of plastocyanin and Y>4 cCuCl42. ...

Figure 7. Ground-state wave function of plastocyanin. A HOMO wave function contour for plastocyanin (28). B HOMO wave function contour for the thiolate copper complex tet b (34/ C Copper L-edge (38) and sulfur K-edge (34) spectra as probes of metal-ligand covalency. D Absorption, single-crystal polarized absorption, and low-temperature MCD spectra of plastocyanin. The absorption spectrum has been Gaussian resolved into its component bands as in reference 33.

Fig. 12a-d. Visible and near-IR spectra of plastocyanin (adapted from Ref. 35) a Absorption spectrum of films at 270 K (solid line) and 35 K (dashed line) lower curves refer to left-hand scale, upper curves to right-hand scale, b Gaussian resolution of the 35 K absorption spectrum, c Circular dichroism spectrum of plastocyanin in pD = 6 deuterated phosphate buffer at 290 K. d Magnetic circular dichroism spectrum of plastocyanin in deuterated phosphate buffer at 290 K... 

Fig. 7. The Gaussian resolution of the Cu(II) UV-VIS absorption spectrum (25 K) of spinach plastocyanin, as in Ref 56. The eighth band is not resolved in this spectrum.

Fig. 2. Absorption spectrum of plastocyanin. Figure source Katoh (1982) Plastocyanin, in CRC Handbook of Biosoiar Resources, Voi 1, Basic Principles, p 162. CRC Press.

Fig. 9. Room-temperature absorption spectrum of spinach Cytbe in the presence of dithionite (A) reduced-minus-oxidized difference spectra as indicated for spinach Cyt bg compiex measured at room temperature in (A) inset and at low temperature (77 K) in (B) (C) 77 K difference spectra of the isolated (spinach) Cyt bef complex titrated to the potentials indicated. See text for details. Figure source (A) and (B) Hurt and Hauska (1981) A cytochrome flb complex of five polypeptides with plastoquinol-plastocyanin-oxidoreductase activity from spinach chloroplasts. Eur J Biochem 117 594 (C) Hurt and Hauska (1983) Cytochrome /) from isolated cytochrome complexes. Evidence for two spectral forms with different midpoint potentials. FEBS Lett 153 415.

Durell SR, Lee C, Ross RT, Gross EL, Factor analysis of the near-ultraviolet absorption spectrum of plastocyanin using bilinear, trilinear, and quadrilinear models, Archives of Biochemistry and Biophysics, 1990, 278, 148-160. 

Finally, we will discuss the electronic spectra of blue copper proteins. The absorption spectrum of plastocyanin, the best studied blue copper protein, is dominated by a bright band at 16,700 cm (600 nm), giving rise to its bright blue color. However, a more thorough investigation of the experimental spectrum identifies at least six more absorption bands below 22,000 cm , as is shown in Table 4. Several different methods have been used to interpret this spectrum, ranging from the semi-empirical CNDO/S method, over various DFT methods (Xa and time-dependent... 

But oxidized plastocyanin are also known to exhibit a very peculiar absorption spectrum, characterized by a veiy intense absorption at about 600 nm responsible for the intense blue color, and quite different from the one of isolated copper com-... 

Fig. 1.3 Structure left) and computed absorption spectrum right) of plastocyanin. For the spectrum wavelengths in nm and intensities in arbitrary units...

Recently, the effect of the mutation of the methionine ligand on the absorption spectrum of the blue-copper proteins has been underlined and proved experimentally [13], as well as the artificial mutation of the active site loop sequence of plastocyanin with the nitrosocyanin one giving rise to a red-copper protein [31]. 

The additional effects in the aromatic region of the difference spectrum (250-300 nm) are probably caused by aromatic transitions which are influenced by the redox state of the copper. The shoulder at 270 nm, which occurs in all three proteins, could result from an increase in tyrosine absorption. In this context, it is interesting to recall that Tyr 108 (azurin numbering), which is relatively close to the proposed copper ligands Cys 112 and Met 121, is completely invariant both in azurin and plastocyanin and may therefore be an obligatory constituent of the copper site. 

Plastocyanin contains two copper atoms per molecule. Plastocyanin in photosystem I is soluble in the lumen region and can be readily released in a hypotonic medium and purified by DEAF chromatography. In the oxidized form the copper protein is blue with a major absorption band at 597 nm = 4.7 mM two weaker absorption bands at 460 and 770 nm, and one band with vibrational structure characteristic of amino acids in the ultraviolet region (see Fig. 2). Plastocyanin in the reduced state does not absorb in the visible region. The low-temperature EPR spectrum of oxidized PC has characteristic g-values at 2.05 and 2.23. 

The following amino acids have been definitely excluded as part of a common structure of the Type 1 center Tryptophan has been eliminated as a ligand for the reasons given in Section IIAl. Arginine is absent in the plastocyanins. Tyrosine has been eliminated by optical absorption studies of azurin and by a recent analysis of the resonance enhanced Raman spectrum of stellacyanin 206). 

In Figs. 4 and 5, we report the TD-DFT computed spectra of wild-type plastocyanin and nitrosocyanin, respectively. One can immediately see that the UVAdS spectrum of plastocyanin is dominated by the intense absorption at about 600 nm, responsible for the blue color of the protein some weaker structures appear at shorter and longer... 

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