Functional and Structural Properties of the 50,000 D Subunit of Octopus Vulgaris Hemocyanin

Abstract

Although the functional and structural properties of hemocyanins (Hc) have been well characterized (1,2), the interpretation of the results is often difficult owing to the quite complicated quaternary structure of these copper proteins. Under physiological conditions, Octopus vulgaris Hc exists as a large aggregate with a sedimentation coefficient s ^°_20,w = 50 S (MW=2.7×10⁶). The smallest component which can be obtained without splitting covalent bonds (by increasing the pH or in the presence of 3 M urea) has s ^°_20,w = 11 S (MW=250,000) (3). A fully functional component with s = 5 S (MW=50,000), corresponding to the theoretical minimal subunit, has been obtained from O. vulgaris He after proteolysis with trypsin under controlled conditions. The functional and conformational properties of 5 S subunit have been compared with those of the protein in the two main aggregation states (11S, 50S). A definite picture of the tryptophan (Trp) residues localization can be obtained with no interference of the quaternary structure.