Nitrate reductase inactivating factor from rice cells in suspension culture

With a crude extract of cultured rice cells, there was no directrelationship between the activity of NADH nitrate reductasemeasured and the amount of cell extract used, when the amountwas large. It appeared that some factor in the cell extractinactivated nitrate reductase. The inactivating factor couldbe separated from nitrate reductase by (NH₄)₂SO₄ precipitation.The factor seemed to be protein: 1) it was precipitable with(NH₄)₂SO₄ heat labile, and pronase treatment caused loss ofactivity; 2) cycloheximide reduced the formation of the inactivatingfactor. The activity of this factor fluctuated during the growthperiod. The existence of this inactivating factor was furtherinvestigated in various other cultured cells. (Received December 1, 1975; )