The biosynthesis of CMP-Sia in mammals. Sialic acid (Sia) is a nonulosonic amino sugar with a carboxylate at the C1 position that is ionized at physiological pH giving it a negative charge. Sia is synthesized in the cytosol and is activated in the form of CMP-Sia in the nucleus. The CMP-Sia is transported to the cytosol by an unknown mechanism and subsequently to the Golgi lumen by the CMP-Sia transporter (CMP-SiaTr) where it serves as a donor substrate to sialyltransferases (STs) that incorporate it at the nonreducing end of mature glycans. CMP: cytidine monophosphate.
