Typical gastropod hemocyanin decamer (a, b), and extracted subunit dimer (a', b'). In a and b, one out of five subunit dimers is transparent to reveal the underlying molecular model of KLH1 published recently . The 3D volume shown here in grey was calculated from this molecular model at 9-Å resolution. Red lines in a' and b' mark the borderline between the two constituent 400 kDa subunits, each encompassing eight different functional units (red, FU-a; yellow, FU-b; green, FU-c; orange, FU-d; purple, FU-e; blue, FU-f; cyan, FU-g; gold, FU-h). Note that FU-a to FU-f form the cylinder wall, whereas FU-g and FU-h constitute the collar complex. Although the two subunits are identical in primary structure, they are folded into two different conformations to form an asymmetric homo-dimer .