ISSN:
1075-4261
Keywords:
cytochrome ba3
;
cytochrome aa3
;
binuclear site structure
;
cyanide
;
Raman spectroscopy
;
normal coordinates
;
Chemistry
;
Analytical Chemistry and Spectroscopy
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Biology
,
Physics
Notes:
The cyanide isotope-sensitive low-frequency vibrations of ferrous cyano complexes of cytochrome a3 are studied for cytochrome ba3 from Thermus thermophilus and cytochrome aa3 from bovine heart. Cyanide complexes of ba3 display three isotope sensitive frequencies at 512, 485, and 473 cm-1. The first is primarily an Fe - C stretching motion, whereas the lower wavenumber modes are bending motions. These iron-cyanide vibrations are independent of the redox levels of the other metal centers in the protein. On the other hand, the fully reduced bovine derivative complexed with cyanide gives rise to a bending vibration at 503 cm-1 and a stretching vibration at 469 cm-1. That is, the ordering of the stretching and bending frequencies is reversed from that of the bacterial protein. These results are analyzed by normal coordinate calculations to obtain comparative models for the binuclear O2 reducing site of the two proteins. We find that the observed frequencies are consistent with a linear Fe - C - N group and larger Fe - C stretching force constant (2.558 mdyn/Å) for ba3 and a slightly bent Fe - C - N group (angle ∼ 170°) and a smaller Fe - C stretching force constant (2.335 mdyn/Å) for aa3. Thus, there are significant differences in the interaction of cyanide with ferrous a3 in the two proteins that are most likely caused by a weaker proximal histidine interaction and stronger peripheral heme electron withdrawing effects in ba3. Possible sources of these protein-induced effects are discussed. Using the analysis developed here, comparison of the FeCN stretching and bending frequencies of the ferrous bovine a3-CN complex to those obtained from the ferric a3-CN complex suggests that upon conversion of the resting to the fully reduced protein, a conformational change occurs that constrains the ligand binding site. © 1998 John Wiley & Sons, Inc. Biospectroscopy 4: 1-15, 1998
Additional Material:
4 Ill.
Type of Medium:
Electronic Resource
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