A request was made of Grith Sorensen and Jack Griffith who graciously produced the SP-D and the image (respectively) which is quite different than the SP-D dodecamers that were shadowed by Ed Crouch years ago.

I am working to find out what differs in the technique for shadowing. This is a clean image but does not have the oversized CRD shadowed on the ends of each of the trimers and the N termini junction in the center is no where near as lumpy as images of Crouch et al.

Size measurements on this dodecamer do fit nicely with previous measurements for shadowed SP-D.  upper left=original image, upper right, cut out of the dodecamer as I WAS IT; lower left, segmented line measurements of two hexamers separately, red line=85.61nm (so a little short); green line=119388nm; diameter (touching three of the four CRD=115.20nm. Lower right is just a coloring of the dodecamer – as i see it.

and a new set of measures is seen below…..   a different diameter – touching three CRD position which does change the mean diameter of this SP-D.