Temperature dependence of nitrate reductase in the psychrophilic unicellular alga Koliella antarctica and the mesophilic alga Chlorella sorokiniana.

Temperature responses of nitrate reductase (NR) were studied in the psychrophilic unicellular alga, Koliella antarctica, and in the mesophilic species, Chlorella sorokiniana. Enzymes from both species were purified to near homogeneity by Blue Sepharose (Pharmacia, Uppsala, Sweden) affinity chromatography and high-resolution anion-exchange chromatography (MonoQ; Pharmacia; Uppsala, Sweden). Both enzymes have a subunit molecular mass of 100 kDa, and K.

Observations on enzymes of ammonia assimilation in two different strains of Cyanidium caldarium.

Two strains of Cyanidium caldarium, one able to utilize nitrate as a substrate, and the other not, were tested for the presence of enzymes of ammonia assimilation. The nitrate-assimilating strain exhibits glutamate dehydrogenase activity. By contrast, the other strain lacks glutamate dehydrogenase; it possesses high alanine dehydrogenase and L-alanine aminotransferase activities which suggest that this strain may incorporate ammonia through reductive amination of pyruvate and may form glutamate from 2-ketoglutarate by a transamination reaction with alanine.