Hemocyanins in spiders, XVI[1]. Subunit topography and a model of the quaternary structure of Eurypelma hemocyanin.

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.