Nucleotide sugars isolation

The occurrence of amino acids in the uridine nucleotides originally isolated by Park suggests that these compounds are involved in the activation or condensation of amino acids, but no enzymatic reactions of these compounds are known. A specific function in the formation of bacterial cell walls has been suggested following the finding of similar ratios of D-glutamic acid, D- and u-alanine, lysine, and amino sugar (1 3 1 1) in cell walls and a uridine nucleotide, both isolated from Staphylococcus aureus. ... 

The same conclusion was drawn by Nelsestuen and Kirkwood (1971) who investigated the mechanism of the E. coli enzyme with UDP-4-keto-6-deoxyglucose and TDP-4-keto-6-deoxyglucose as substrates. The enzyme was reduced with NaB H4, yielding a product which contained tritium-labeled DPNH. Addition of the substrate led to rapid oxidation of the epimerase and to the formation of nucleotide sugars, from which fu-cose and quinovose were isolated after acid hydrolysis. Degradation of the sugars showed that the label was present exclusively in position 4. 

Since none of these enzymes have been extensively purified, they are differentiated from one another primarily by the nature of the acceptor and by the linkage synthesized. TTie general reaction catalyzed by the sialyl-transferases is shown in Fig. 9. Although at least four different sialic acids have been described (Gottschalk, 1960a), only two nucleotide sugar derivatives have been isolated, namely, CMP-2V-acetylneuraminic acid and CMP-N-glycolylneuraminic acid it is presently not known whether different enzymes catalyze the transfer of these two different N-acylneu-raminic acids and most of the sialyltransferase literature is limited to the more readily available CMP-N-acetylneuraminic acid. 

Table 1. Summary of nucleotide sugar transport activities identified in Golgi- and ER fractions and genes that have been isolated so far.

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