On the Role of Individual Subunits in the Quaternary Structure of Crustacean Hemocyanins
Among crustaceans, a widespread hemocyanin aggregate is the dodecamer (24S), composed of two hexameric halfs. According to computer correspondence analysis data (Bijlholt, unpublished), a one-point contact between the two hexamers is probable. A special subunit is required acting as inter-hexamer linker. In the dodecameric 24S hemocyanins of the crayfishes Cherax destructor and Astacus leptodactylus, a disulfide bridged dimer plays this role (1,2). Accordingly, heptameric intermediates were observed when Astacus dodecamers were stepwise dissociated into subunits. In contrast, dodecamers from the crab Cancer pagurus and the lobster Homarus americanus pass hexameric dissociation intermediates, and no dimers were found (3). One particular subunit, designated as alpha’, is absent in native 16S hemocyanin of Cancer, and forms dimers under reassociation conditions (4). Apart from the bridging unit, additional subunit types form the two basic hexamers in 24S crustacean hemocyanins. Although X-ray data on the spiny lobster, Panulirus interruptus hemocyanin afforded a deep insight into the conformation of a 16S particle (5), the question remains whether or not those “hexamer-formers” are structurally equivalent and interchangeable. Recently, new data on subunit correspondencies of crustacean hemocyanins became available, resulting in a definition of the immunological subunit types alpha, beta, and gamma (6). This now enables a better interspecific comparison of the results of our earlier (4) and the more recent experiments about reassembly and immuno labeling. They were performed with hemocyanin subunits from the brachyuran crabs Cancerpagurus and Callinectessapidus , and the astacuran crayfishes Homarus americanus and Astacus leptodactylus .
KeywordsQuaternary Structure Spiny Lobster Gamma Subunit Subunit Type Monomeric Subunit
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- 2.Markl J. & Kempter B. (1981): J.Comp.Physiol. 141, 594–502.Google Scholar
- 4.Markl J., Stöcker W., Runzler R., Kempter B., Bijlholt M.M.C. & van Bruggen E.F.J. (1983): In: Structure and function of invertebrate oxygen binding proteins (Wood E.J., ed.). Life Chem. Reports 1, 39–42.Google Scholar
- 6.Markl J., Stöcker W., Runzler R. & Precht E. (1986): This volume,pp. 281–292.Google Scholar
- 7.Markl J., Hofer A., Bauer G., Markl A., Kempter B., Brenzinger M. & Linzen B. (1979): J.Comp.Physiol. 133, 167–175.Google Scholar