Band 3 protein of the red cell membrane of the llama: Crosslinking and cleavage of the cytoplasmic domain

Comparative studies were done on the cytoplasmic domain of the band 3 protein in the red cell membranes of the the human and the llama. Two approaches were used: crosslinking with o-phenanthroline/CuSO₄, and cleavage with 2-nitro-5-thiocyano-benzoate. o-Phenanthroline/CuSO₄ crosslinks the band 3 polypeptide chains in the human; in contrast band 3 in the llama is minimally crosslinked by this agent. 2-Nitro-5-thiocyano-benzoate cleaves band 3 in the human into a 23,000-dalton fragment; a similar fragment is not generated from the llama band 3. These studies show that the cysteine residue located 23,000 daltons from the N-terminus of band 3 in the human involved in these reactions is unavailable for crosslinking and cleavage in the llama. Species differences in the cytoplasmic domain of band 3 may contribute to the unusual resistance of llama red cells to osmotic, chemical and physically-induced deformation.