Spirulina nitrate-assimilating enzymes (NR, NiR, GS) have higher specific activities and are more stable than those of rice.

Spirulina platensis, a cyanobacterium whose N-metabolic pathway is similar to that of higher plants like rice (Oryza sativa), produces tenfold more protein, indicating a higher capacity for nitrate utilization/removal. Our in vitro analyses in crude extracts revealed that this can be attributed, at least in part, to the higher specific activities (3-6 fold) and half lives (1.2-4.4 fold) of the N-assimilating enzymes, nitrate reductase (NR), nitrite reductase (NiR) and glutamine synthetase (GS) in Spirulina.