Structural and functional polymorphism of the hemocyanin O 2 transport system of the sand fiddler crab Uca pugilator

Abstract

Uca pugilator hemocyanin is an exceptionally heterogeneous aggregate of different polypcptide chains. In a sample of < 100 individuals as many as nine different monomers were resolved. As reported by earlier workers, this protein is also exceptionally polymorphic. Only two of the nine chains in the present sample were invariant. Seven chains varied both qualitatively and quantitatively. Five of the variable chains never reached the highest quantities attained by the other four. Phenotypes lacking one of the two variable chains that did reach maximal quantities, and/or one of the chains that reached intermediate quantities, were chosen for measurements of respiratory properties. The results strongly suggest that the more major of these two chains has a large influence on O 2 affinity and a small influence on its pH dependence. Therefore, the structural polymorphism is accompanied by functional differences as well.