Structure and properties of hemocyanins: XII. Electron microscopy of dissociation products of Helix pomatia α-hemocyanin: Quaternary structure

Abstract

Electron microscopy of the dissociation products of α-hemocyanin of the snail Helix pomatia reveals two distinctly different conformations of 1 10 -size molecules: a C(compact)-form at high ionic strength and pH near 8, and an L(loose)-form at low ionic strength and/or higher pH. The size and shape of the C- 1 10 -size molecules indicate a dissociation of the 1 2 -size molecules along the (10,9) helical grooves, which have been shown to be boundaries between the morphological units of the cylinder wall (Mellema & Klug, 1972). The 5-fold collar is distributed evenly among the C- 1 10 -size molecules. The C → L conformational change is characterized by a drastic loosening of the 1 10 -size molecules to a flexible cluster of globules, with a concomitant decrease of sedimentation coefficient and increase of intrinsic viscosity and frictional ratio. The 1 20 -size molecule appears as a flexible, linear chain of seven or eight globules with a diameter of 55 to 60 Å. These globules are inferred to be the minimal oxygen binding units with a molecular weight of about 50,000, linked together by short stretches of the polypeptide chain. Stable intermediate dissociation products, 2 10 , 3 10 and 4 10 -size molecules, were obtained by intramolecular crosslinking of 1 2 -size molecules with dimethyl-suberimidate prior to dissociation.