Hemes a and a3 environments of plant cytochrome c oxidase.
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.
de Paula
J C
JC
Department of Chemistry, Michigan State University, East Lansing 48824.
Peiffer
W E
WE
Ingle
R T
RT
Centeno
J A
JA
Ferguson-Miller
S
S
Babcock
G T
GT
D003576:Electron Transport Complex IV / Q000737:chemistry*; D006418:Heme / Q000737:chemistry*; D010940:Plant Proteins / Q000737:chemistry*; D011522:Protons; D013059:Spectrum Analysis, Raman; D014908:Triticum / Q000201:enzymology; D003313:Zea mays / Q000201:enzymology
D010940:Plant Proteins; D011522:Protons; D006418:Heme; D003576:Electron Transport Complex IV