Overview of ManNAc analog metabolism <i>via</i> sialic acid metabolism and glycosylation (SAMG) gene activity.

<p>‘High-flux’ ManNAc analogs (1,3,4-O-Bu₃ManNAc, 1,3,4-O-Bu₃ManNAz, 1,3,4-O-Bu₃ManNAl analogs) passively diffuse across the plasma membrane after which the core natural or R-modified ManNAc (i.e., ManNAc, ManNAz, or ManNAl) is released <i>via</i> non-specific carboxylesterases (<i>CES</i>) that hydrolyze the butyrate groups. ManNAc(R) is converted to sialic acids by the kinase activity of <i>GNE</i> and subsequent activities of <i>NANS</i>, and <i>NANP</i> in the cytosol; in this study these metabolites constitute ‘Compartment 1’ and are measured in aggregate using the periodate resorcinol assay. Once synthesized and dephosphorylated, sialic acid enters the nucleus where it is converted to the corresponding nucleotide sugar (e.g., CMP-Neu5Ac, CMP-Sia5Az, or CMP-Sia5Al) by <i>CMAS</i>; these activated sialic acids are then transported into the Golgi apparatus by <i>SLC35A1</i> and <i>SLC35A3</i> where a subset of the 20 human sialyltransferases created sialoglycoconjugates (primarily, N- and O- linked glyocoproteins or gangliosides [i.e., sialic acid-modified glycosphingolipids]) and these compounds constitute ‘Compartment 2’ and are also measured in aggregate using the periodate resorcinol assay (as outlined in the Materials and Methods section).