Glutamine synthetase ofChlamydomonas: its role in the control of nitrate assimilation

摘要

Work is described which suggests that glutamine synthetase (GS) could play an important and direct regulatory role in the control of NO3assimilation by the alga. In both steady-state cells and ones disturbed physiologically by changes in light or nitrogen supply the assimilation of NO3appears to be limited by the activity of GS. Moreover although in normal cells NH3can completely inhibit NO3uptake, promote the deactivation of nitrate reductase (NR) and repress the synthesis of NR and nitrite reductase (NIR), these controls are relaxed in cells in which GS is deactivated by treatment with L-methionine-DL-sulfoximine (MSO). It is proposed that the reversible deactivation of GS may play an important part in the regulation of NO3assimilation although it is still not clear whether the enzyme itself or products of its metabolism are responsible.