The pentaammineruthenium(III)-histidine complex in ribonuclease A as an optical probe of conformational change

Preparation and characterization of pentaammineruthenium-(histidine-83)azurin: thermodynamics of intramolecular electron transfer from ruthenium to copper

The reaction between a5RuH2O2+ (a is NH3) and Pseudomonas aeruginosa azurin at pH 7, followed by oxidation, yields a5Ru(His-83)3+-azurin(Cu2+) as the major product. Spectroscopic measurements (UV-visible, CD, EPR, and resonance Raman) indicate that the native structure is maintained in the modified protein. The site of ruthenium binding (His-83) was identified by peptide mapping. The a5RuHis/Cu ratio in the modified protein, determined from the EPR spectrum, is 1:1, and the reduction potentials (vs. normal hydrogen electrode, pH 7.0, 25 degrees C) are blue copper (Cu2+/1+), 320 +/- 2 mV; a5Ru(His-83)3+/2+, 50 +/- 10 mV. From measurements of the reduction potentials at several temperatures in the 5-40 degrees C range, delta H degree for intramolecular Ru2+ ----Cu2+ electron transfer was estimated to be -12.4 kcal mol-1 (1 cal = 4.184 J). Analysis of kinetic data in light of the electron transfer exothermicity indicates that the reorganizational enthalpy of the blue copper site can be no larger than 7.1 kcal mol-1.

Preparation and characterization of a pentaammineruthenium(III) derivative of horse heart ferricytochrome c

A stable complex between pentaammineruthenium(III) and histidine-33 in horse heart ferricytochrome c is formed in the reaction between aquopentaammineruthenium(II) and the protein at pH 7. HPLC of the tryptic hydrolysate of the modified protein was employed to identify the pentaammineruthenium binding site. Spectroscopic measurements show that the integrity of the native structure in the vicinity of the heme c group is maintained in the ruthenium-modified protein. The reduction potentials are: heme c (Fe3+/2+), 0.26 V; Ru(NH3)5(His-33)3+/2+, 0.15 V (vs. normal hydrogen electrode).

Interresidue distance measurements in proteins. Fluorescent energy transfer between tryptophans and a Ru(III)(NH3)5-histidine complex in alpha-lytic protease and lysozyme

The mechanism by which the intrinsic fluorescence of tryptophan residues in alpha-lytic protease and lysozyme are quenched by a complex formed between the single histidine residue in each protein and Ru(III)(NH3)5 was investigated. The R0 values for alpha-lytic protease and lysozyme were 15.5 and 11.8 A, respectively. Good agreement between the efficiency of energy transfer measured experimentally and that calculated from the X-ray data, assuming the Förster dipole-dipole mechanism, demonstrates that this mechanism is appropriate. The ease with which the ruthenium-labeled enzymes can be synthesized and purified suggests that the Ru(III)(NH3)5-His complex may have general utility in structural studies of proteins in solution.