On the role of dimeric subunits in the quaternary structure of arthropod hemocyanins.

Partial alkaline dissociation of 24 S (12-meric), 35 S (24-meric) and 60 S (48-meric) hemocyanin from various arthropods was studied by polyacrylamide gradient gel electrophoresis and, in some cases, by electron microscopy. If there are no stable dimers among the subunits, dissociation starts by cleavage of interhexamer bonds, leading to intermediates which are hexamers or multiples of hexamers. Whenever a hemocyanin contained stable dimers, inter-hexamer bonds were also very stable as indicated by the formation of 30 S (19-meric) or 18 S (7-eric) intermediates as primary products. In such cases, inter-hexamer bonds could be cleaved by treatment with reducing agents or with 4M urea; correspondingly, these agents also cleaved the respective dimers into the constituent polypeptide chains. It is concluded that in all cases the dimeric subunits function as bridges between hexamers.