Time resolved optical spectroscopy in photodissociation experiments and molecular dynamics simulations are being used to investigate protein folding and structure function relations in heme proteins. Fast events in the folding of cytochrome c are being studied by optically triggering the folding reaction with nanosecond laser pulses. Before folding begins transient binding of both non-native and native ligands from the unfolded polypeptide has been observed on a microsecond time scale. We have confirmed the prediction from our previous studies on the viscosity dependence of the conformational relaxation in myoglobin that the low temperature behavior of myoglobin with a """"""""frozen"""""""" distribution of conformational substates can be mimicked in a room temperature glass, including the observation of a wide distribution of geminate rebinding rates and spectral changes caused by kinetic hole burning. Extensive modelling of the geminate rebinding and conformational relaxation kinetics of human hemoglobin show that a satisfactory explanation of a very demanding set of data can be explained by a two- state allosteric model. A laser-photolysis light-scattering technique has been used to monitor intracellular hemoglobin S polymerization in sickle cell disease patients before and after treatment with hydroxyurea. Hydroxyurea therapy leads to a reduction in the fraction of rapidly sickling cells, and an increase in the fraction of non-sickling cells expected from the increase in F cells. The median delay time, however, is still smaller than that observed in SC patients, suggesting that a major therapeutic effect from hydroxyurea should not be expected.
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