Regulation by ammonia of nitrate reductase synthesis and activity in [formula omitted

Abstract

In the green alga Chlamydomonas reinhardi , all the enzymes of the nitrate-reducing system are nutritionally repressed by ammonia. Besides, ammonia promotes in vivo the reversible inactivation of nitrate reductase in an indirect way by primarily raising the cellular level of reducing power, which in turn determines the reversible reduction of the enzyme. Subsequent removal of ammonia from the medium causes reactivation of the inactive enzyme. Interconversion of the active and inactive forms into one another can also be directly achieved in vitro by reducing and oxidizing nitrate reductase with its own physiological substrates.