Sialyltransferases of developing rat brain

The activity of four different sialyltransferases acting on N- or O-linked chains of glycoproteins was studied in brains of 19 days-old embryos, 1-day-old newborns and adult rats. By using asialofetuin, fetuin and N-acetyllactosamine as acceptors, it has been possible to measure independently the following enzyme activities: CMP-NeuAc:Gal beta 1-3GalNAc alpha(2-3)-sialyltransferase (EC 2.4.99.4), CMP-NeuAc:Gal beta 1-4GlcNAc alpha(2-3)-sialyltransferase (EC 2.4.99.6), CMP-NeuAc:Gal beta 1-4GlcNAc alpha(2-6)-sialyltransferase (EC 2.4.99.1) and CMP-NeuAc:NeuAc alpha 2-3Gal beta 1-3GalNAc alpha(2-6)-sialyltransferase (EC 2.4.99.7). The specific activity of the first three enzymes which act on asialylated acceptors showed a 2.6-fold decrease in a parallel manner after ontogenic development, while the activity of NeuAc alpha 2-3Gal beta 1-3GalNAc alpha(2-6)-sialyltransferase was four times lower in adult than in embryonic brain, showing a stronger dependence on ontogenic development. Despite the higher level of sialyltransferases able to act on glycoproteins, in fetal brain these glycoproteins do not contain a higher amount of sialic acid.