The alkaline transition in the blue copper protein stellacyanin

VILA, A.J.; SANNAZZARO, A.I.

Amsterdam - Holanda

Congreso; XII International Biophysics Congress; 1996

Interantional Union of Pure and Applied Biophysics

Blue copper proteins (BCP’s) are electron transfer proteins characterized by uncommon spectroscopic features. In stellacyanin (St), the metal ion is coordinated to a Cys, NO His, and a Gln residue. We have studied a reversible transition in St at high pH values not displayed by any other BCP. Methods: This transition was studied in Cu(II)- and Co(II)-substituted St by means of electronic and paramagnetic ‘H NMR spectroscopy. Results: The LMCT bands in Cu(II)St show a frequency shift and intensity variation at alkaline PH. Two distinct alkaline transitions were detected. Similar transitions were observed by following the d-d transitions in the electronicspectrum of Co(II)St. The NMR data indicated major changes in the bound Gln signals. Conclusions: These results indicate an alteration of the metal-cysteine bond. The driving force forthis change is attributed to a conformational rearrangement of Gin 97, that may rotate aroundthe Cp-CT bond to change from oxygen (low pH) to nitrogen coordination (high pH).