Heme a and a3 environments of plant cytochrome c oxidase

Abstract

The structures of hemes a and a3 of maize and wheat germ cytochrome c oxidase were investigated by resonance Raman spectroscopy. Comparison between the plant and mammalian cytochrome oxidases revealed that (i) the vinyl groups associated with hemes a and a3 vibrate at higher frequencies in the plant enzyme than in the mammalian enzyme, suggesting different degrees of interaction between the heme cores and their periphery; (ii) aside from the geometry of the vinyl group, the structure of heme a3 in plant cytochrome oxidase is essentially unchanged from that of its mammalian counterpart; (iii) the vibrational band associated with the formyl group of reduced heme a shows relatively weak enhancement in the Soret-excited resonance Raman spectra of maize and wheat germ cytochrome oxidase, suggesting that the formyl group of ferrous heme a in the plant enzymes is conjugated only slightly to the porphyrin ring; and (iv) for oxidized heme a, the formyl vibration is strongly enhanced, but its frequency indicates a weaker interaction with the protein milieu relative to the mammalian enzyme. These observations suggest that the local environment around the formyl position of the heme a chromophore differs in the plant and mammalian cytochrome oxidases. The implication of the latter feature in the mechanism of proton pumping by cytochrome oxidase is discussed.

Redox-linked transient deprotonation at the binuclear site in the aa 3 -type quinol oxidase from Acidianus ambivalens : Implications for proton translocation

“…However, a time-dependent change subsequently occurs in the Raman spectrum, involving a slow shift in frequency of the formyl stretching mode of heme a 3 , from 1,660 to 1,667 cm Ϫ1 . Immediately after reduction, the frequency of the a 3 formyl stretching mode (1,660 cm Ϫ1 ) observed in this enzyme is the lowest among the heme a 3 -containing oxidases, where this mode occurs in the 1,662 to 1,669 cm Ϫ1 range (26)(27)(28)(29)(30)(31)(32)(33)(34)(35)(36)(37)(38). The absence of spectral changes in the other modes, including the oxidation state marker, 4 , at 1,355 cm Ϫ1 (data not shown), indicates that the oxidation, coordination, and spin states are not changing as a function of time after reduction in either of the hemes.…”

A cooperative model for protonmotive heme‐copper oxidases. The role of heme a in the proton pump of cytochrome c oxidase

“…It may be recalled that involvement of a protolytic group linked to heme a in the proton pump of cytochrome c oxidase had already been proposed by Artzabanov et al [28]and Wikström [29]. A role in proton pumping was also advocated for the formyl substituent of heme a , hydrogen‐bonded to a protolytic residue in the protein [30]. Rousseau et al [31]presented resonance Raman spectroscopic evidence for the presence of H 2 O molecules near heme a and proposed that these H 2 O molecules could shuttle protons from the N aqueous phase to protolytic group(s) whose p K is governed by the redox state of heme a .…”

Photoperturbation of the heme a3-CuB binuclear center of cytochrome c oxidase CO complex observed by Fourier transform infrared spectroscopy

“…The formyl group at the 8-position on the porphyrin ring of heme a3 provides a molecular probe of such interactions. Although the formyl group is a weak scatterer, it has been studied by resonance Raman spectroscopy, and frequency assignments have been made from heme A and from purified cytochrome c oxidase (Salmeen et al, 1973;Callahan and Babcock, 1983;Babcock and Callahan, 1983;de Paula et al, 1990;Ching et al, 1985;Argade et al, 1985;Sassaroli et al, 1988;Choi et al, 1983). Suggestions have been presented that the formyl group of heme A in cytochrome oxidase may be hydrogen bonded to a protein group, and/or the formyl group may be sensitive to conformational changes in the protein (Sassaroli et al, 1988).…”