Scanning transmission electron microscopic study of molluscan hemocyanins in various aggregation states: comparison with light scattering molecular weights

The masses of individual particles of the hemocyanins of six members of two molluscan classes, Polyplacophora and Gastropods, have been determined by scanning transmission electron microscopy (STEM) of unstained specimens dried from the frozen state. The decameric hemocyanins of two chitons, Mopalia muscosa and Stenoplax conapicua, had masses of 4.20 ± 0.18 and 4.47 ± 0.56 MDa, respectively; the didecameric hemocyanins of two gastropods, Fasciolaria tulipa and Pleuroploca gigantea, had masses of 8.67 ± 0.44 and 8.96 ± 0.39 MDa, respectively; and the tridecameric hemocyanin of Lunatia heros had a mass of 13.50 ± 0.44 MDa. The STEM values were in close agreement with those obtained by light scattering measurements of the same samples in solution. For Busycon centrarium, a gastropod with a multidecameric hemocyanin, nine size classes from didecamers to decadecamers with masses that corresponded to multiples of a basic decamer (4.4 MDa) were detected. The appearance of unstained specimens of the cylindrical particles differs from negatively stained specimens. Viewed end-on the cylinders show no internal structure, but in well-preserved specimens cavities are apparent in the side views of the cylinders that resemble those seen in negatively stained specimens. Although they lack the characteristic “tiered” appearance, the number of decameric units can be counted and their arrangement within the particle seen.