Fig. 1.

De novo synthesis and recycling pathways of UDP-sugars. Enzymes, 1 UDP-glucose dehydrogenase (UGD); 2 myo-inositol-oxygenase (MIOX); 3 glucuronic acid-1-kinase (Glucuronokinase); 4 UDP-sugar pyrophosphorylase (USP); 5 arabinose-1-kinase (Arabinokinase); 6 putative xylose-1-kinase (not known); 7 galacturonic acid-1-kinase; 8 galactose-1-P kinase (Galactokinase); 9 UDP-glucuronic acid 4-epimerase; 10 UDP-xylose synthase; 11 UDP-apiose synthase; 12 UDP-xylose epimerase; the “de novo synthesis/recycling” pathway including inositol-1-P, inositol, glucuronic acid, and glucuronic acid-1-P is also referred to as “Inositol oxygenation pathway”