Comparison of 5′‐Nucleotidase Activities Among Cultured Murine Melanoma Cell Lines

The activity of 5′-nucleotidase and ouabain-sensitive Na/K ATPase was determined in seven different mouse melanoma cell lines. Ouabain-sensitive Na/K ATPase activity was found in NP40-treated cell homogenates of all cell lines. However, 5′-nucleotidase activity was found in only one mouse melanoma cell line—JB/RH. The absence of expression of 5′-nucleotidase activity in the other six cell lines is not associated with pigmentation in melanoma cells, nor is the gene switched off in all transformed melanocytes of C57BL/6 origin.