Angular scattering analysis of the circular dichroism of biological cells. 1. The red blood cell membrane.

A quantitative interpretation of the distorted circular dichroism spectrum of red blood cell membranes is presented including the effects of the intense small angle scattering and light detection geometry of our spectrophotometers. Corrected spectra have been obtained by nondestructive methods which correspond to an in situ membrane protein conformation of 45% alpha helix, 10% beta sheet, and a conformational precision of better than +/- 10%. Forward scattering calculations which neglect the small angle scattering collected by conventional phototube acceptance angles are shown to be unsuitable for red cell membranes. Ultraviolet refractive index dispersion has been estimated for the membranes together with an evaluation of the sensitivity of the calculated spectrum to this variable. Angular scattering and circular dichroism calculations are extended to two alternative models for the location of hemoglobin in "pink ghosts", and it is indicated that this approach might help in resolving the question whether residual hemoglobin is in solution inside the ghost, or is part of its membrane.