Regulation of Nitrite Reductase Activity under CO2 Limitation in the Cyanobacterium Synechococcus sp. PCC7942.

AUTOR(ES)

Suzuki, I.

RESUMO

During photoautotrophic growth under CO2-limited conditions, cells of Synechococcus sp. PCC7942 excreted into the medium about 30% of the nitrite produced by reduction of nitrate. No nitrite was excreted under CO2-sufficient conditions. After transfer of high-CO2-grown cells to CO2-limited conditions, nitrite reductase activity started to decline within 0.5 h and decreased to 50% of the initial level in 3 h, whereas nitrate reductase activity was virtually unchanged. Nitrite started to accumulate in the medium about 3 h after the transfer of the cells to CO2-limited conditions and reached a concentration of >0.4 mM at 17 h. These findings suggested that the nitrite excretion was due to an imbalance of the activities of nitrite reductase and nitrate reductase. Since ammonium, the product of nitrite reduction, was not detected in the medium, it was concluded that the step of nitrite reduction limits the rate of nitrate assimilation under CO2-limited conditions. The extent of decrease in nitrite reductase activity under CO2-limited conditions was much larger than that caused by rifampicin (an inhibitor of RNA synthesis) treatment under high-CO2 conditions. Addition of CO2, in the form of sodium bicarbonate, to the CO2-limited culture increased the nitrite reductase activity, but rifampicin inhibited this increase. These findings suggested the presence of a mechanism that irreversibly inactivates nitrite reductase under CO2-limited conditions.

Documentos Relacionados

• Nitrite-Specific Active Transport System of the Cyanobacterium Synechococcus sp. Strain PCC 7942
• MapA, an iron-regulated, cytoplasmic membrane protein in the cyanobacterium Synechococcus sp. strain PCC7942.
• Molecular structure and enzymatic function of lycopene cyclase from the cyanobacterium Synechococcus sp strain PCC7942.
• Cloning, nucleotide sequence, and mutagenesis of a gene (irpA) involved in iron-deficient growth of the cyanobacterium Synechococcus sp. strain PCC7942.
• Ethoxyzolamide Inhibition of CO2 Uptake in the Cyanobacterium Synechococcus PCC7942 without Apparent Inhibition of Internal Carbonic Anhydrase Activity 1