Sialylation of Thomsen-Friedenreich (T) and blood type NM antigens by transferases in human sera measured by [14C]NAN uptake.

Human erythrocyte T & NN antigens were exposed to fresh sera from single human donors and CMP-[14C]sialic acid without activators in a single 24 hr incubation at 37 degrees C. There was similar sialic acid (NAN) uptake, on the average 2.7 mol/mol T antigen subunit (mol wt 40,000), with various NN- and MM-derived T antigens and transferase sera in all different combinations. Sera from donors with the M gene but not from those lacking it incorporated NAN into NN antigen (c. 1 mol NAN/mol NN antigen subunit, mol wt 50,000). The profound difference in sialyltransferase action between sera from donors with the M gene and those lacking it was substantiated by repeated incubations of NN-derived T antigen with CMP-NAN and MM donor transferase serum, which incorporated 32% more NAN than did repeated incubations of the same antigen with CMP-NAN and NN donor transferase serum. The greater NAN incorporation by sera of donors with the M gene is due to an additional transferase-modifier substance present only in persons possessing the M gene.