DETAILED ANALYSIS OF THE CHARGE-TRANSFER BANDS OF A BLUE COPPER PROTEIN - STUDIES OF THE NICKEL(II), MANGANESE(II), AND COBALT(II) DERIVATIVES OF AZURIN

The preparation and characterization of the manganese(II) and nickel(II) derivatives of the blue copper protein azurin (Pseudomonas aeruginosa) are described. The circular dichroic spectra of the nickel(H) and cobalt(II) derivatives are reported and are correlated with that of native azurin. The results of fluorescence, absorption, and competitive binding experiments indicate that all metals coordinate at the copper binding site. Ligand optical electronegativities are computed from the charge-transfer spectra of the cobalt(II), nickel(II), and copper(II) proteins, and transitions from a cysteine sulfur and a methionine sulfur are identified. Bands maximizing at 560 (130 M-1cm-1), 442 (3300 M-1cm-1), and 360 nm (1570 M-1cm-1) in the absorption spectrum of the nickel(ll) derivative are assigned as πS(Cys) Ni(II), σS(Met) → Ni(II), and σS(Met) Ni(II) charge-transfer bands, respectively. Corresponding assignments are proposed for bands of native azurin which appear at 820, 626, and 467 nm, respectively. © 1979, American Chemical Society. All rights reserved.