An experimental method correcting for absorption flattening and scattering in suspensions of absorbing particles: circular dichroism and absorption spectra of hemoglobin in situ in red blood cells.

An experimental approach to interpretation of the anomalous absorption and circular dichroism (CD) spectra of hemoglobin in situ in red blood cells is reported. Absorption flattening effects have been overcome by use of high cell concentratons in very short light path cuvettes. Differential scattering contributions to circular dichroism have been resolved using a CD instrument capable of variable detection geometry. Scattering effects have also been resolved using media of high refractive index to match that of the red blood cell. The results are in agreement with a parellel calculational analysis of red blood cell CD spectra, which predicted the relative magnitudes of the flattening and differential scattering CD contributions. An experimental absorption spectrum has been obtained for hemoglobin in the red blood cell with scattering and flattening eliminated. This quantitatively simulates the spectrum of a hemoglobin solution. The methods described should be widely applicable to conformational studies of macromolecules in their native environment.