Naslov
Iron-Carbon Bond Lengths in Carbonmonoxy and Cyanmet Complexes of the Monomeric Hemoglobin III from Chironomus thummi thummi: A Critical Comparison between Resonance Raman and X-Ray Diffraction Studies

Autori
Yu, Nai-Teng ; Benko, Bojan ; Kerr, Ellen A. ; Gersonde, Klaus

Izvornik
Proceedings of the National Academy of Sciences of the United States of America (0027-8424) 81 (1984), 4; 5106-5110

Vrsta, podvrsta i kategorija rada
Radovi u časopisima, članak, znanstveni

Ključne riječi
Bond angle ; Bond length ; Chironomus thummi ; Carbon monoxyde ; Cyanide ; Isotope shift ; Haemoglobin ; Resonance Raman ; X-ray

Sažetak
Soret-excited resonance Raman spectroscopy yields direct information regarding the iron-carbon bonding interactions in the cyanomet and carbonmonoxy complexes of hemoglobin III from Chironomus thummi thummi (CTT III) in solution. By isotope exchange in cyanide (13CN-, C15N-, and 13C15N-) and carbon monoxide (13CO, C18O, and 13C18O), we have assigned the Fe(III)– CN- stretching at 453 cm-1, the Fe(III)– C– N- bending at 412 cm-1, the Fe(II)– CO stretching at 500 cm- 1, the Fe(II)– C– O bending at 574 cm-1, and the C– O stretching at 1960 cm-1. The resonance Raman data, in conjunction with those obtained from heme model complexes with well-known Fe– C bond distances, strongly suggest that the Fe(III)– CN- bond (approximately 1.91 Å ; ; ) is longer (hence weaker) than the Fe(II)– CO bond (approximately 1.80 Å ; ; ). This result disagrees with those of x-ray crystallographic studies [Steigemann, W. & Weber, E. (1979) J. Mol. Biol. 127, 309-338] in which the Fe– C bond lengths were reported as 2.2 Å ; ; in cyanomet and 2.4 Å ; ; in carbonmonoxy CTT III. Based on Badger's rule and normal mode calculations, the x-ray data would lead to the prediction of 279 cm-1 for the Fe(II)– CO stretching frequency in CTT III• CO, which was not observed. On the other hand, we estimate the Fe– CO bond as approximately equal to 1.82 Å ; ; , which is very similar to the 1.80 Å ; ; value in human Hb• CO crystals. Furthermore, we have used isotope shift data to estimate the Fe– C– O angle as 169± ; ; 5°, somewhat larger than the 161° value found by Steigemann and Weber. We therefore conclude that there must be errors in the x-ray crystallographic refinement for the ligand geometry in carbonmonoxy and cyanomet CTT III.

Izvorni jezik
Engleski

Znanstvena područja
Fizika, Kemija, Biologija

POVEZANOST RADA