Temperature-jump studies and polarized absorption spectroscopy of methemoglobin-thiocyanate single crystals.
Steinhoff HJ, Schrader J, Schlitter J
Association equilibria and association kinetics of the thiocyanate binding
reaction to methemoglobin in single crystals and solution are studied using
temperature-jump technique and polarized absorption spectroscopy. Different
kinetic constants are found for the reaction in solution and crystal phase
for the alpha- and beta-subunits of the methemoglobin tetramer. The reduction
of the reactivity of the alpha- and beta-subunits in crystalline phase
is 6-fold and 2.4-fold, respectively, compared to the values found in solution.
The intramolecular binding reaction of the N epsilon of the distal histidine
E7 which is observed in methemoglobin in solution cannot be detected in
single crystals. Our results suggest that crystallization of hemoglobin
has little influence on small-scale structural fluctuations which are necessary
for ligands to get to the binding sites and large-scale structural motions