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-sialyltr ansferase (ST3Gal I) and Gal beta 1,4GlcNAc cu 2,6-sialyltransferase ( ST6Gal I) from both chicken and mouse, CMP-NeuAc and CMP-NeuGc were co mpared as donor substrates with pyridylamino-oligosaccharides as accep ters. ST6Gal I showed 4-7-times higher activity toward CMP-NeuGc than CMP-NeuAc, while for ST3Gal I there was no significant difference betw een them, irrespective of the origin of the enzymes. Also, the differe nce in donor substrate (i.e., NeuAc and NeuGc) had little effect on th e preference to acceptor substrates of these enzymes. Thus, the result s 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 l east partly, explain the discrepancy in the ratio of NeuAc and NeuGc i n glycolipids and glycoproteins in individual tissues.