Identification of the phosphorylation site on human erythrocyte band 7 integral membrane protein: implications for a monotopic protein structure.

Band 7 membrane protein was metabolically labelled with [32P]phosphate in the presence of cAMP, isolated and digested, the labelled peptides were purified and sequenced. Ser-9 was identified as the only phosphorylation site. This proves that the N-terminal region is located at the cytoplasmic side of the membrane and implies a monotopic rather than the predicted bitopic structure.