Resistance of bovine band 3, a hydrophobic erythrocyte membrane protein, to denaturation of guanidine hydrochloride.

Bovine Band 3 was cleaved into two fragments by extracellular chymotryptic attack. As in the case of intact Band 3, both fragments were resistant to complete denaturation by guanidine hydrochloride and did not show the single cooperative conformational transition which is typical of many globular proteins. These results suggest that each Band 3 fragment contains several domains differing in resistance to denaturation. A discriminant function analysis further suggests that a considerable part of the polypeptide chain of the fragments is intercalated into or interacts with the lipid bilayer. These combined data are not incompatible with the suggestion of Drickamer ((1977) J. Biol. Chem. 252, 6909-6917) that the Band 3 polypeptide is probably folded to pass several times through the membrane.