Negative staining characteristics of arrays of mitochondrial pore protein: use of correspondence analysis to classify...

Fourier-filtered images of negatively stained arrays of mitochondrial pore protein have been classified by correspondence analysis of their diffraction patterns. The most significant component of interpattern variation is an isotropic shift in reflection intensities between high- and low-order reflections. This corresponds in the images to the presence or absence of high resolution detail (stain minima). Experimentally the loss of detail in images correlates with the use of highly dissociated heavy metal salts as negative stains. It is proposed that such stains yield poorer negative-contrast images due to electrostatic binding of heavy-metal complex ions to fixed charge groups on the protein. Results with surface-modified protein arrays are consistent with this hypothesis.