Subunit Structure of Hemocyanin from the Gastropod Levantina hierosolima

Abstract

Electron microscopy and hydrodynamic studies have shown that gastropod hemocyanin can exist in a number of discrete states of aggregation 100, 60, 20 and 11 S that have been identified as 1 (whole), 1/2, 1/10 and 1/20 molecules (1,2). The 11 S species, which corresponds to the fully dissociated polypeptide chain, has in turn been shown to consist of 8 functional units, similar in size, each carrying a binuclear copper centre (3,4). The molecular weight of the 100 S native molecule has been determined to be ~9×10⁶ (Archachatina marginata, 9.08×10⁶ (5); Busycon canaliculatum, 8.8×10⁶ (6); Helix pomatia, 8.95×10⁶ (7), Helix pomatia α, 8.91×10⁶ (5), Helix pomatia β, 8.95×10⁶ (5), 9.02×10⁶ (8), 7.55×10⁶ (9)). A molecular weight of 55 000 has been determined for Helix pomatia functional unit (3,10). From these findings, a molecular weight of ~450 000 has been predicted for the polypeptide chain of gastropod hemocyanin ((1/20)×9×10⁶ or 8×55 000). However, the molecular weight determined for the polypeptide chain is ~350 000 (Busycon canaliculatum 300 000 (6); Helix pomatia α, 365 000 (11) and 330 000 (12), Helix pomatia β, 350 000 (8)). The reason for the discrepancy could, a priori, be in the molecular weight determination of the functional unit, the polypeptide chain or the native molecule; it could also involve an error in the number of functional units per polypeptide chain or the number of polypeptide chains per 100 S molecule. The solution to this problem provided the motivation for this study.