A study of an erythrocyte membrane protein that contributes to inhibition of agglutination of feline erythrocytes in glucose solution

Due to the negative charges on their surface membrane, erythrocytes usually do not agglutinate each other in vivo. However, when mixed with 5% glucose solution in a test tube, some feline erythrocytes exhibit agglutination. To investigate the reasons for this phenomenon, we extracted erythrocyte membrane proteins from these cells and subjected them to sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). In samples in which agglutination did not occur, a band was seen at the 36-kDa position, whereas in samples showing agglutination, this band disappeared or has lower intensity. The 36-kDa position corresponds to glycophorin A in the human erythrocyte membrane, but no immunochemical cross-reaction with this band was seen. We therefore conducted mass spectrometry in order to investigate the composition, and found a partial amino acid sequence, His-Ile-Thr-Ser-Tyr-Pro-Glu-Thr-His-Glu-Gly. Furthermore, although no protein showing this sequence was found in any database, this protein was confirmed to be an acidic glycoprotein, therefore it is thought to be a glycophorin-like molecule in the feline erythrocyte membrane that could contribute to inhibition of agglutination.