| Abstract: | The relative activities of tyrosine hydroxylase, aromatic-l -amino-acid decarboxylase and dopamine beta-hydroxylase were established in a number of clones of neuroblastoma cells isolated from the uncloned mouse C-1300 tumor. One clone, NBD-2, was chosen for further analysis on the basis of its relatively high activities of tyrosine hydroxylase and dopamine beta-hydroxylase. The levels of these enzymes, and monoamine oxidase and catechol O-methyltransferase, were at least 20-80 fold lower in the neuroblastoma culture than in mouse superior cervical ganglion. More importantly, aromatic-l -amino-acid decarboxylase activity was not even detectable in any neuroblastoma clone examined. Based on the relative sensitivities of the tyrosine hydroxylase and aromatic-l -amino-acid decarboxylase assays and on the ratio of these two enzymes in the mouse ganglion, decarboxylase activity is more than 10 fold lower in the cultured cells than would be predicted on the basis of tyrosine hydroxylase activity. Dialysis and mixing studies with neuroblastoma extracts and partially purified aromatic-l -amino-acid decarboxylase did not reveal the presence of any endogenous inhibitors that could account for the low level of decarboxylase activity in the cultured cells. During growth of the neuroblastoma cells to confluency, only one enzyme, monoamine oxidase, exhibited an elevated specific activity on the basis of cell number. However, when based on the amount of protein, the specific activity of all measurable enzymes increased in culture-because cell protein decreased 5 fold during growth to confluency. These findings are discussed with respect to individual cell function. |
