Fig. 1.

Two models for the repeating unit in the feather keratin filament. The colored spheres delineate the approximate localities of the sidechains of emu feather (green, hydrophobic; pale blue, hydrogen-bonding; red, acidic; dark blue, basic; yellow, half-cystine; grey, glycine). The upper views correspond to Structure A and the lower views to a possible alternative Structure B. a and d are projections down the diad (x-axis), b and e are projections down the y-axis, and c and f are projections down the axis of the filament (z-axis)