J. Biol. Chem., Vol. 261, Issue 24, 10960-10962, Aug, 1986
Ultraviolet Raman spectroscopy indicates fast (less than 7 ns) R----T- like motion in hemoglobin
S Dasgupta, RA Copeland and TG Spiro
Raman spectra of oxy- and deoxyhemoglobin obtained with 218 and 200 nm
pulsed (7 ns) laser excitation show changes (loss of 880 cm-1 tryptophan
band intensity, increase in the 830/850 cm-1 tyrosine doublet intensity
ratio) which are attributed to the aromatic contacts (Trp beta 37-Tyr alpha
140 and Tyr alpha 42-Asp beta 99) that are specific to the T quaternary
structure. At high concentration (2 mM in heme) HbCO shows the same
spectral signatures as HbO2. As the HbCO concentration is decreased,
however, the spectra approach those shown by deoxy-Hb. This dilution effect
is attributable to photolysis, which increases with decreasing
concentration. The results imply that the HbCO photoproduct shows the same
aromatic environments as does deoxy- Hb. Thus, T-like contacts are
apparently formed at the alpha 1 beta 2 interface within 7 ns of
photolysis, a time short compared to the spectral alterations of the heme
group (approximately 100 ns, approximately 1 microsecond, and approximately
20 microseconds) which have previously been attributed to tertiary and
quaternary relaxations.
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