Enzymatic Hydrolysis of Uridine Diphosphate-N-acetyl-d-galactosamine and Uridine Diphosphate-N-acetyl-d-glucosamine by Normal Cells, and Blocks in This Hydrolysis in Transformed Cells and Their Revertants

The two sugar nucleotides, UDP-N-acetyl-d-galactosamine and UDP-N-acetyl-d-glucosamine, are enzymatically hydrolyzed by normal hamster cell extracts to yield free N-acetyl-d-galactosamine and N-acetyl-d-glucosamine, respectively. A nucleotide pyrophosphatase activity splits the sugar nucleotides to UMP and the appropriate N-acetyl-d-hexosamine-1-phosphate, and another enzymatic step with orthophosphoric monoester phosphohydrolase activity then hydrolyzes the phosphorylated intermediate sugar to free N-acetyl-d-hexosamine. The two enzymatic activities differ in their divalent ion requirement and optimal pH and show the same hydrolytic activity on both sugar nucleotides. Different lines of hamster transformed cells and their revertants showed a block in either one or the other enzyme. Cell lines transformed by Rous sarcoma virus or Simian virus 40 were blocked in the nucleotide pyrophosphatase activity, whereas cell lines transformed by polyoma virus or after treatment with the chemical carcinogen dimethylnitrosamine were blocked in the second phosphohydrolase step. Variants from the polyoma- and dimethylnitrosamine-transformed cells, which had reverted in the biological properties characteristic of transformation, showed the same enzymatic block as their parental transformed cells. The block in enzyme activities may thus be due to a common genetic change in transformed cells and their revertants that is not found in the normal cells.