Properties of the Trypsinised Red Cell Receptor Reacting in Reversible Agglutination by Normal Sera

Inhibition experiments and studies with isotope labelled trypsin confirmed that the reversible reaction between trypsinised human red cells and trypsin agglutinin in normal sera is weakly inhibited by trypsin and that trypsin is adsorbed to the red cells during enzyme treatment. However, large concentrations of trypsin were needed for inhibition, and human trypsin agglutinin did not react with trypsin adsorbed to rabbit red cells. It therefore seems unlikely that the trypsin agglutinin receptor on human red cells is identical with trypsin adsorbed to the cell membrane. Trypsinised red cells treated with various proteolytic enzymes, β‐galactosidase and periodate, were no longer agglutinated by purified trypsin agglutinin. These findings indicate that the trypsin agglutinin receptor is a glycoprotein.