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

Abstract

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

Nitrate assimilatory enzymes of Spirulina (Arthospira) platensis are more thermotolerant than those of rice

“…Our earlier studies have shown that NR in Spirulina is substrate-inducible (Jha et al, 2007), a fact well known in higher plants but not in non-nitrogenfixing, nitrate-dependent cyanobacteria. We also showed that NR, NiR and GS in Spirulina have higher specific activities and stabilities at room temperature than those from rice (Ali et al, 2008). The present study was aimed at examining the thermotolerance of NR, NiR and GS in vitro in Spirulina, compared to those of rice, since higher plants are traditional sources for these enzymes.…”

“…Panvel 1) were obtained as described earlier (Ali et al, 2008), surface-sterilized, imbibed in distilled water and grown on washed wet cotton in plastic trays at 28 °C and 80 % humidity under white light (1 Klux, 12 hour diurnal cycle) for 9 days. Excised leaves were floated on 40 mM KNO 3 for 6 hrs, frozen in liquid N 2 and stored at -70 °C till use.…”

“…Excised leaves were floated on 40 mM KNO 3 for 6 hrs, frozen in liquid N 2 and stored at -70 °C till use. Crude extracts were prepared as described earlier (Ali et al, 2008).…”

“…Nitrate reductase specific activity was measured as described earlier for Spirulina (Jha et al, 2007) and rice (Ali et al, (2008). It was defined as nmoles of nitrite produced per mg protein per min.…”

“…Nitrite reductase activity in both the organisms was assayed as described by Ali et al (2008). The reaction mixture contained 75 mM potassium phosphate buffer (pH -7.5), 0.5 mM KNO 2 , 2 mM methyl viologen, 20 mM Na 2 S 2 O 4 freshly prepared in 0.3 M sodium bicarbonate and 50 l of enzyme extract.…”