I am still working to determine the nature of the protein inclusion in the rough endoplasmic reticulum of some type II pneumocytes (alveolar type II cells) in guinea pigs from an experimental series that was conducted in the 1980s testing whether toluene diisocyanate was harmful for human health. These protein inclusions, I am hoping are going to turn out to be indicators of overproduction of surfactant protein A, or maybe D, though less likely SP-D, because SP-A is the most abundant surfactant protein in lung according to many reports). The protein itself, appears to be so organized I have called paracrystalline, and has not to my knowledge been described in detail, save for a couple of brief descriptions in the early 1980’s literature.

The protein displays several bands, typically parallel to the long axis of the rough endoplasmic reticulum membrane boundaries, which I have shown before, but in this short video clip I have examined the possibility of their being a periodicity to the protein, in the parallel axis to the membranes of the RER, by superimposing five images, removing the light (background) areas, and increasing contrast in the dark areas.

If one accepts that the distance from one dark band to the other (in this case the plasmalemma) is 100 nm,  then I think there is a relatively obvious periodicity of about  4 dense areas within the central band (middle between two dark bands), that is, within about the same 100 nm length.