The subunit characterization of Callinectes sapidus hemocyanin.

Hemocyanin from the blue crab, Callinectes sapidus, sediments at 25.7 S and has a native molecular weight of 940 000 +/- 20 000. Under solution conditions of increased pH (approximately 10) or ionic strength, the native molecule dissociates to a 17 S species. Reversal of this dissociation was unsuccessful. At pH 10 and with the removal of Mg2+, the 17 S species reversibly dissociates to form a subunit species which sediments at 6 S. A comparison of the circular dichroic spectra of the 25.7 S and 6 S hemocyanins suggests that little happens to the structural integrity of the polypeptide backbone upon the two dissociations. Molecular weight estimations under reducing and denaturing conditions indicate that the 6 S hemocyanin species represents the constituent polypeptide chain of the protein molecule. Chemical analysis suggests the presence of a small amount, less than 3%, of carbohydrate bound to the polypeptide chain. Electrophoresis of the hemocyanin in the presence of sodium dodecyl sulfate or urea reveals two major electrophoretic species of either slightly different chemical composition or slightly different polypeptide chain length.