The effect of driving force on intramolecular electron transfer in proteins. Studies on single-site mutated azurins (original) (raw)

1992, European Journal of Biochemistry

An intramolecular electron-transfer process has previously been shown to take place between the Cys3 -Cys26 radical-ion (RSSR-) produced pulse radiolytically and the Cu(I1) ion in the blue singlecopper protein, azurin [Farver, 0. & Pecht, I. (1 989) Proc. Nut1 Acad. Sci. USA 86, further investigate the nature of this long-range electron transfcr (LRET) proceeding within the protein matnx, we have now investigated it in two azurins where amino acids have been substituted by single-site mutation of the wild-type Pseudomonas aeruginosa azurin. In one mutated protein, a methionine residue (Met44) that is proximal to the copper coordination sphere has been replaced by a positively charged lysyl residue ([M44K]azurin), while in the second mutant, another residue neighbouring the Cu-coordination site (His35) has been replaced by a glutamine ([H35Q]azurin). Though both these substitutions are not in the microenvironment separating the electron donor and acceptor, they were expected to affect the LRET rate because of their effect on the redox potential of thc copper sitc and thus on the driving force of the reaction, as well as on the reorganization energies of the copper site.