Subunit heterogeneity of Cancer magister hemocyanin

Hemocyanin from the Dungeness crab, Cancer magister, has been described as a 25-S two-hexamer assembly of two different 5-S subunits. We have found that at least six different 5-S polypeptide chains constitute this hemocyanin. They can be separated from one another by sodium dodecyl sulfate slab gel electrophoresis as well as by regular gel electrophoresis. The six 5-S polypeptides appear very different from one another when each SDS-treated subunit is partially digested with Staphylococcus aureus V8 protease. This pattern of six subunits is present both in hemolymph which has been examined immediately upon removal from the animal as well as in hemocyanin which has remained at room temperature for two weeks. Thus, it is unlikely that the heterogeneity is a result of proteolysis during preparation of the sample. Possible implications of the high degree of subunit heterogeneity on the protein's quaternary structure are discussed.