Biosynthetic nucleotide sugars

NUCLEOTIDE SUGARS ACT AS SUGAR DONORS IN MANY BIOSYNTHETIC REACTIONS... 

As a complement to the comprehensive Chapter on the biosynthesis of complex saccharides by Nikaido and Hassid in Vol. 26, where the products of biosynthesis were stressed, Kochetkov and Shibaev (Moscow) here emphasize the nucleotide sugar biosynthetic intermediates, themselves, in a detailed article on their chemistry and enzymology. 

Biosynthetic pathways for nucleotide sugars. [Reproduced with permission from H. Schachter, Glycoprotein biosynthesis. In The Glycoconjugates, Vol. 2, M.I. Horowitz and W. Pigman (Eds). Academic Press,... 

T0 biosynthetically or chemoenzymatically prepare unnatural sialosides, the unnatural Sias must first be converted to nucleotide sugar donors. CMP-Sia synthetases catalyze the reaction of Sia with CTP to yield CMP-Sia and pyrophosphate (Figure 22). The E. coli synthetase is commonly used in chemoenzymatic... 

In the overwhelming majority of cases, the nucleotide sugars appear to be the immediate precursors of the glycoprotein-bound sugars, but evidence has been accumulating in recent years for the participation of lipid intermediates in certain of the biosynthetic reactions. In particular, incorporation of mannose into glycoproteins may take place via a lipid intermediate, and the details of this process will be discussed later (see Section IV, A, 5, b). 

The simple carbohydrates and monosaccharides produced by photosynthetic reactions serve as precursors of more complex molecules produced from them by a variety of biosynthetic pathways. Carbohydrates such as sucrose and the more complex polysaccharide starch are usually considered as direct products of photosynthesis and are synthesised in reactions involving nucleotide sugars as intermediates. 

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