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Partial alkaline dissociation of 24 S (12-meric), 35 S (24-meric) and 60 S (48-meric) hemocyanin from various arthropods was studied by polyacrylamide gradient gel electrophoresis and, in some cases, by electron microscopy. If there are no stable dimers among the subunits, dissociation starts by cleavage of interhexamer bonds, leading to intermediates which are hexamers or multiples of hexamers. Whenever a hemocyanin contained stable dimers, inter-hexamer bonds were also very stable as indicated by the formation of 30 S (19-meric) or 18 S (7-eric) intermediates as primary products. In such cases, inter-hexamer bonds could be cleaved by treatment with reducing agents or with 4M urea; correspondingly, these agents also cleaved the respective dimers into the constituent polypeptide chains. It is concluded that in all cases the dimeric subunits function as bridges between hexamers.

Specific antibodies were prepared against the individual subunits of the hemocyanin isolated from the tarantula Eurypelma californicum. From the antibodies, the monovalent antigen-binding fragments (Fab) were made by papain treatment. Native 37S hemocyanin was incubated with individual Fab species and the labelling of the seven subunits (a, b, c, d, e, f and g) analyzed by electron microscopy. Specific labelling patterns were found for each Fab, which allowed the allocation of specific positions to each subunit within the (4 x 6)-subunit oligomer. Along the large cleft which separates the two dodecameric half-molecules, subunits f, b, c, f are located; e forms the four corners of the 37S particle, while a is found on both sides of the small cleft which separates the two hexamers within each dodecamer, d is close to a on the outer long edges, and g close to f at the side of the particle. These results and those obtained previously by means of partial dissociation and reassembly experiments, confirm and support each other, allowing the construction of a model of the quaternary structure of Eurypelma hemocyanin.