Control by Glutamine of the Synthesis of Nitrate Reductase in Cultured Spinach Cells

Abstract

Immunoblotting, using antibodies raised against electrophoretically pure nitrate reductase, was used to study the regulation of synthesis of nitrate reductase in cultured spinach cells. The extent of the loss of nitrate reductase activity that occurred when cultures were transferred to a glutamine-containing medium was correlated with the decrease in the level of cross-reacting material (repression). Removal of exogenous glutamine resulted in the appearance of nitrate reductase activity as well as of immunoreactive protein (derepression). The activity of nitrate reductase in spinach cells under “repressing” or “derepressing” conditions appears to be regulated by changes in the amount of the enzyme protein rather than by inactivation and activation of preexisting protein.