[Glutamate dehydrogenases of unicellular green algae: effects of nitrate and ammonium in vivo]

The constitution and control by the inorganic nitrogen source of glutamate dehydrogenases of some unicellular green algae have been studied. The Ankistrodesmus braunii and Scenedesmus obliquus cells contain two different glutamate dehydrogenases, one of which is NADP-specific, the other is active with both NAD and NADP. Their synthesis does not depend on the nitrogen source. The activity of NADP-specific glutamate dehydrogenase increases sharply during nitrogen starvation. In Chlorella pyrenoidosa 82 and Ch. ellipsoidea only one constitutive double specific glutamate dehydrogenase is observed. Its activity does not change depending on the nitrogen nutrition conditions. In the cells of the thermophylic Chlorella strain Chlorella sp. K. ammomium induces a de novo synthesis of NADP-specific glutamate dehydrogenase in addition to the constitutive double specific glutamate dehydrogenase. Thus, the algae tested contain constitutive double specific glutamate dehydrogenase. The NADP-specific enzyme is absent in two Chlorella strains, is constitutive in A. braunii and S. obliquus, and is ammonium-inducible in three thermophylic Chlorella strains.