Nucleotide sugar intermediates, synthesis

Pathway 2, Reactions involved in synthesis of the nucleotide sugar intermediates. These reactions are documented in the following references Kai cjear and Maxwell (1958), Pogell and Gryder (1957), Chou and Soodak (1952), Davidson et al. (1957), Leloir and Card ini (1956), Maley et al. (1956), Cardini and Leloir (1957), Comb and Roseman (1958), Ghosh and Roseman (1961, 1962), Warren and Felsenfeld (1961, 1962), Roseman (1962) and Glaser (1963). 

Several nucleotides have been detected in milk (see Table 1.9). The list includes the common mono-and dinucleotides, 3, 5 cyclic AMP, and adenosine triphosphate (ATP). The ATP is located entirely in the casein micelles (Richardson et al. 1980). Several nucleotide sugars, undoubtedly excess intermediates left over from mammary synthesis of glycoproteins, are present. Both DNA and RNA have been detected in milk (Swope and Brunner 1965 Swope et al. 1965 Langen 1967) they are probably found primarily in milk leukocytes. 

UDP-GlcNAc represents the branching point for the bacterial biosynthesis of murein and lipopolysaccharides where secondary nucleotide sugars are involved [329, 358], Starting from fructose-6-P, all enzymes are available as recombinant proteins and enzymatic synthesis of important intermediates seems to be possible. 

Sequential biocatalytic cascade reactions are characterized by the use of multiple enzymatic steps involving various biocatalysts. One cascade reaction can consist of an enzyme-module with several enzymes if substrate and inhibitor kinetics are compatible with these combinations. Sequential use of such enzyme-modules surpassing the work-up of intermediate products is the criterion for the idea of cascade reactions we address here on the one hand, the synthesis of nucleotide sugars and their derivatives, on the other hand, the synthesis of glycan epitopes with multiple GTs. 

Biosynthesis of UMP. The parts of the intermediates derived from aspartate are shown in red. Bold type indicates atoms derived from carbamoyl phosphate. In contrast to purine nucleotide synthesis, where ring formation starts on the sugar, in pyrimidine biosynthesis the pyrimidine ring is completed before being attached to the ribose. 

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