Resonance Raman Detection of the Fe²⁺−C−N Modes in Heme−Copper Oxidases:  A Probe of the Active Site

Abstract

Resonance Raman spectroscopy has been employed to investigate the reduced cyano complexes of cytochrome aa(3) from bovine heart and Rhodobacter sphaeroides and of cytochrome bo(3) from E. coli. In the aa(3)-type oxidases, the frequency of the Fe-CN stretching mode is located at 468 cm(-1), and the bending Fe-C-N vibration, at 500 cm(-1). The fully reduced cytochrome bo(3)-CN complex gives rise to a stretching vibration at 468 cm(-1), a bending vibration at 491 cm(-1), and a stretching C-N vibration at 2037 cm(-1). The observed differences between aa(3) and bo(3) oxidases in the frequencies of the Fe-C-N group suggest a quantitative difference in the structure of the His-heme a(3)(2+)/Cu(B)(1+) and His-heme o(3)(2+)/Cu(B)(1+) binuclear pockets upon CN- binding.

Long distance electron transfer in cytochrome c oxidase immobilised on electrodes. A surface enhanced resonance Raman spectroscopic study

“…Cyanide binding to solubilised CcO has been extensively studied previously using UV-Vis absorption as well as IR and resonance Raman spectroscopy. [31][32][33][34][35][36][37][38][39] To immobilise the fully oxidised cyanide complex of CcO (CcO[CN]), the enzyme was incubated with a 200-fold excess of cyanide for 1 h prior to immobilisation. Also during the individual steps of the immobilisation procedure, a 200-fold excess of cyanide was maintained.…”

Characterisation of the Cyanate Inhibited State of Cytochrome c Oxidase

“…Inhibition of the binuclear center (BNC) has been shown in the past using different organic ions such as cyanide (CN − ), sulfide (S 2− ) or azide (N 3 − , which is isoelectronic to NCO − ) [2][3][4][5][6][7]12,59 . The involved excess electrons in this process could lead to partial heme reduction and consequently to the rise of the Soret band at around 444 nm 60,61 .…”

“…For example, a bridging peroxide (O 2 2− ) has been proposed to exist in the resting state of CcO 1 that requires two more electrons to get fully reduced than the oxidized state during catalytic turnover. Intense research has been performed on cyanide [2][3][4][5][6][7] (CN − ) ligands that effectively block the BNC for oxygen. While this inhibition of CcO is a central subject in medical research on cyanide poisoning [8][9][10][11] , spectroscopic studies on the binding properties of ligands such as cyanide, azide (N 3 − ) or sulphide (S 2− ) 2,12,13 have been performed to derive the oxygen reduction mechanism, to get insight into the structure of the active site 2,5,6,14 and for spectral isolation of the two heme centers [15][16][17][18] .…”

Oxygen Metabolism in the Lung

“…A unique factor affecting heme-containing dioxygenases, however, is that they can be strongly inhibited by small molecules or ions, such as NO, CO, cyanide, and H 2 S. These compounds can bind tightly to iron in the nonheme complex. Inhibition by such molecules results from blocking the necessary interaction of O 2 with the transition metal center and may represent a critical form of cellular regulation of these processes (Kolluru et al, 2013;Foresti and Motterlini, 2010;Pinakoulaki et al, 2004). Since there is a great variety in the reactions catalyzed by oxygenases that have the same or similar cofactors, how and if these small molecular weight inhibitors can act with specificity is not clear, a factor that is critical to their role as signal transduction elements.…”