Structure and properties of hemocyanins. XII. Electron microscopy of dissociation products of Helix pomatia alpha-hemocyanin: quaternary structure |
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Authors: | R J Siezen E F van Bruggen |
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Affiliation: | Biochemisch Laboratorium, Rijksuniversiteit, Groningen, The Netherlands |
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Abstract: | Electron microscopy of the dissociation products of α-hemocyanin of the snail Helix pomatia reveals two distinctly different conformations of -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--size molecules indicate a dissociation of the -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--size molecules.The C → L conformational change is characterized by a drastic loosening of the -size molecules to a flexible cluster of globules, with a concomitant decrease of sedimentation coefficient and increase of intrinsic viscosity and frictional ratio.The -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, , and -size molecules, were obtained by intramolecular crosslinking of -size molecules with dimethyl-suberimidate prior to dissociation. |
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