A. Heather Good

Three monoclonal antibodies have been raised against partially purified band 4.5 polypeptides [Steck (1974) J. Cell Biol. 62, 1-19] from pig erythrocyte membranes. The antibodies were capable of binding to both intact pig erythrocytes and protein-depleted membrane preparations and recognized detergent-solubilized polypeptides from adult and neonatal pig erythrocytes that were photolabelled with [G-3H]nitrobenzylthioinosine (NBMPR), a potent specific inhibitor of nucleoside transport. The antibodies did not recognize polypeptides from neonatal pig erythrocytes that were photolabelled with the glucose-transport inhibitor [3H]cytochalasin B. Reactivity with polypeptides of apparent Mr 64,000 [10% (w/v) acrylamide gels] was demonstrated by Western-blot analysis. The antibodies recognized pig band 4.5 polypeptides after prolonged treatment with endoglycosidase F, a finding consistent with reactivity against polypeptide, rather than carbohydrate, determinants. Trypsin digestion of NBMPR-labelled protein-depleted pig erythrocyte membranes generated two labelled polypeptide fragments (Mr 43,000 and 26,000). Two of the antibodies recognized both fragments on Western blots, whereas the third bound to the larger, but not to the smaller, fragment. The antibodies had no significant effect on reversible binding of NBMPR to protein-depleted pig erythrocyte membranes and did not bind to NBMPR-labelled polypeptides in human, rabbit or mouse erythrocytes.