Enzyme Regulation in Neuroblastoma Cells

Acetylcholinesterase from mouse neuroblastoma C‐1300 was purified 733 times by affinity chromatography. Antibodies against the purified enzyme were used to select clones with a 100‐times‐lower acetylcholinesterase activity than in an unselected clone. Antibodies against an enzyme located on the surface membrane, can thus be used to select genetic variants with lower enzyme activity. The decrease in acetylcholinesterase activity was not associated with a decrease in choline‐O‐acetyltransferase activity, The two clones that showed a 100‐times difference in acetylcholinesterase activity showed about the same choline‐O‐acetyltransferase activity. This lack of correlation between the activity of these two cholinergic enzymes was also found in clones isolated without using antibodies. The existence of an independent control of these two enzyme activities was further shown by treatment of neuroblastoma cells with adenine, cyclic AMP and dibutyryl cyclic AMP, which increased acetylcholinesterase activity but decreased the activity of choline‐O‐acetyltransferase. There was no effect on either enzyme by treatment with guanine, hypoxanthine, cytidine, or uridine, indicating that adenine plays a specific role in the regulation of these two enzymes. High acetylcholinsterase activity was associated with low saturation density of the cells in tissue culture, and a low affinity to the surface of a tissue‐culture petri dish. It is suggested, that clonal differences in acetylcholinesterase activity and in these two biological properties, can be explained by differences in the structure of the surface membrane.