MACROMOLECULAR ORGANIZATION OF HEMOCYANINS AND APOHEMOCYANINS AS REVEALED BY ELECTRON MICROSCOPY

[摘要] Comparative electron microscopic studies of the structural organization of representative hemocyanins and apohemocyanins from Mollusca and Arthropoda are described. Helix pomatia, Busycon canaliculatum and Loligo pealei were chosen as examples of the Mollusca; Honiara''s americanus and Limulus polyphemus represented the Arthropoda. High-resolution electron microscopy using improved preparation techniques and instrumentation (coherent microbeam illumination) revealed new structural details in the molecules close to quaternary levels. Molluscan hemocyanins are cylindrical molecules (diameter about 340 A, height ranging from 140 to 680 A) built up from 3 to 12 rows of subunits. Arthropodan hemocyanins are built from a cubic monomer (105 [image]) in various stages of organization which is species dependent. Molluscan hemocyanins are distinctly different from Arthropodan hemocyanins, although they seem to be built from analogous subunits. Observations indicating the possible presence of certain constituents specifically localized in the core of the Molluscan hemocyanins are discussed. A differentiated outer layer is regularly found around the hemocyanins and apohemocyanin molecules of Mollusca. It is not known whether these structures are actual components of the native molecules or are determined by the preparation techniques. Their possible presence can have significant biological implications. Reproducible differences between hemocyanins and apohemocyanins were observed in the Mollusca and under certain conditions. The results are discussed in relation to the available biochemical and biophysical data on these highly organized macromolecular complexes.