The induction of ornithine decarboxylase by L-asparagine and intracellular alkalinization

The uptake of transport systems A and N amino acids, most noticeably L-asparagine, is essential for the induction of ornithine decarboxylase (L-ornithine carboxylase, EC 4.1.1.17) in cultured cells and we have proposed that the uptake-associated pH and ionic changes might constitute part of the cell activation signal (1). In the present study, it was shown that extracellular L-asparagine caused an immediate and transient increase in intracellular pH which was continuously monitored by the fluorescence probe BCECF (2',7'-bis(carboxyethyl)-5,6-carboxyfluorescein). NH4Cl and NH4OH which caused intracellular alkalinization also caused ornithine decarboxylase activity to increase.