title: Plastocyanin conformation: the effect of the oxidation state on the pKa of nitrotyrosine-83.
abstract: Plastocyanin treated with tetranitromethane was nitrated at a single location, Tyr-83. Tyr-83 and its neighboring negative charges have been implicated as a binding site for positively charged redox agents (Chapman, S.K., Watson, A.D. and Sykes, A.G. (1983) J. Chem. Soc. Dalton Trans. 1983, 2543-2548). No effect was observed on either the plastocyanin midpoint redox potential or its reaction kinetics with P-700+ and cytochrome f. This makes nitration an ideal spectroscopic probe for monitoring changes in the environment of Tyr-83. The pKa of the nitrotyrosine was 8.6 and 8.3 for reduced and oxidized plastocyanin, respectively, indicating that the charge on the copper atom is 'felt' at Tyr-83. The high pKa value for both forms indicates that Tyr-83 is in a negatively charged environment, near residues Nos. 42-45 and Nos. 59-61. The extinction of the nitrotyrosine chromophore at 360 nm was not affected by a change in redox state. However, the ellipticity of this transition was greater for the oxidized form, indicating that environment of Tyr-83 is dependent upon the charge on the copper atom. This suggests an electrostatically driven conformational change at Tyr-83. A conformational change at Tyr-83 could regulate the binding of plastocyanin with its reaction partners in order to promote smooth electron transport.
mesh_terms: D002734:Chlorophyll / Q000494:pharmacology; D002851:Chromatography, High Pressure Liquid; D002942:Circular Dichroism; D003201:Computers; D003580:Cytochromes / Q000378:metabolism; D045348:Cytochromes f; D005029:Ethylenediamines / Q000494:pharmacology; D007526:Isoelectric Point; D007700:Kinetics; D009566:Nitrates; D010940:Plant Proteins / Q000032:analysis*; D010970:Plastocyanin / Q000032:analysis*; D011487:Protein Conformation; D013056:Spectrophotometry, Ultraviolet; D014443:Tyrosine; D014961:X-Ray Diffraction
chemical_list: D003580:Cytochromes; D005029:Ethylenediamines; D009566:Nitrates; D010940:Plant Proteins; D002734:Chlorophyll; D014443:Tyrosine; C001785:chlorophyll P 700; C031234:ethylenediamine; D010970:Plastocyanin; D045348:Cytochromes f