THE HEMOCYANIN OF THE SQUID SEPIOTEUTHIS-LESSONIANA - STRUCTURAL COMPARISON WITH OTHER CEPHALOPOD HEMOCYANINS

The subunit structure of the hemocyanin from the squid Sepioteuthis le ssoniana has been characterized by analytical sedimentation. The prote in exists free in the hemolymph as a 60S, multisubunit structure with a molecular mass of approximately 4.0 x 10(6) gm/mol. At extremes of p H this can be dissociated into 10 monomers, of mass 3.8 x 10(5) gm/mol each. At neutral pH, if 5 mM Mg2+ or less is present, the monomers as sociate to form a dimer of molecular mass 7.7 x 10(5) gm/mol. In the p H range from 10.5 to 7.5, formation of the dimer is facilitated by the binding of one proton per monomer. If the magnesium concentration is raised to 25 mM or more, the dimers reversibly and completely associat e into decamers. This process is shown to require the binding of 10 ma gnesium ions. In its size, subunit structure, and behavior with respec t to association-dissociation processes, Sepioteuthis hemocyanin resem bles the corresponding proteins of other squid much more than it does those of Octopus or Nautilus. (C) 1997 Elsevier Science Inc.