Affinity labeling of erythrocyte band 3 protein with pyridoxal 5-phosphate. Involvement of the 35,000-dalton fragment in anion transport.

Transport of pyridoxal 5-phosphate (PLP) into erythrocytes was inhibited by inhibitors of anion transport including stilbene disulfonate compounds, indicating that it is mediated by Band 3 protein. When erythrocytes were treated with PLP and large amounts of free lysine and NaBH4, two membrane-spanning fragments of Band 3 (Mr = 17,000 and 35,000) were specifically labeled. When the cells were pretreated with 4,4'-dinitrostilbene 2,2'-disulfonate, the labeling in the 35,000-dalton fragment was inhibited. Erythrocytes labeled by PLP in both the 17,000- and 35,000-dalton fragments transported PLP at a decreased rate, whereas the cells labeled in only the 17,000-dalton fragment had essentially the same transport activity as the control when 4,4'-dinitrostilbene 2,2'-disulfonate was removed. The extent of inhibition of transport of inorganic phosphate in the labeled cells was similar to that of PLP. The results indicate that the 35,000-dalton fragment participates in the anion transport of the cell membrane.