Donor substrate specificities of Gal beta 1,4GlcNAc alpha 2,6-sialyltransferase and Gal beta 1,3GalNAc alpha 2,3-sialyltransferase: comparison of N-acetyl and N-glycolylneuraminic acids.

Using cloned sialyltransferases, Gal beta 1,3GalNAc alpha 2,3-sialyltransferase (ST3Gal I) and Gal beta 1,4GlcNAc alpha 2,6-sialyltransferase (ST6Gal I) from both chicken and mouse, CMP-NeuAc and CMP-NeuGc were compared as donor substrates with pyridylamino-oligo-saccharides as acceptors. ST6Gal I showed 4-7-times higher activity toward CMP-NeuGc than CMP-NeuAc, while for ST3Gal I there was no significant difference between them, irrespective of the origin of the enzymes. Also, the difference in donor substrate (i.e., NeuAc and NeuGc) had little effect on the preference to acceptor substrates of these enzymes. Thus, the results showed that the cloned sialyltransferases can utilize both CMP-NeuAc and CMP-NeuGc as donor substrates, and that the preference difference between the sialyltransferases to CMP-NeuGc and CMP-NeuAc could, at least partly, explain the discrepancy in the ratio of NeuAc and NeuGc in glycolipids and glycoproteins in individual tissues.