In this communication, we have demonstrated that hydrolysis of the nucleotide sugar can cause errors in the detection of an ectoglycosyltransferase. Spleen cell suspensions can incorporate radioactivity when incubated with labeled UDP-galactose, but all the activity is due to decomposition of the nucleotide sugar and uptake of the free sugar. The fibroblast cell lines can incroporate carbohydrate directly from UDP-galactose. Several criteria are presented with can be used to demonstrate that a nucleotide sugar is the direct carbohydrate donor.
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