Nitrate uptake by the halotolerant cyanobacterium Aphanothece halophytica grown under non-stress and salt-stress conditions.
We have compared the characteristics of nitrate uptake by Aphanothece halophytica grown under non-stress and salt-stress conditions. Both cell types showed essentially similar patterns of nitrate uptake toward ammonium, nitrite, and DL-glyceraldehyde. Although the affinities of nitrate to non-stress cells and salt-stress cells were not significantly different, i.e., Ks = 416 and 450 microM, respectively, the V(max) value for non-stress cells was about twofold of that for salt-stress cells (9.1 vs 5.3 micromol min(-1) mg(-1) Chl). Nitrate uptake by A. halophytica was found to be dependent on Na+. Ammonium inhibited nitrate uptake, and the presence of methionine sulfoximine could not release the inhibition by ammonium. Nitrite appeared to competitively inhibit nitrate uptake with a K(i) value of 84 microM. Both chloride and phosphate anions did not affect nitrate uptake. DL-Glyceraldehyde, an inhibitor of CO2 fixation, caused a reduction in the uptake of nitrate.
Incharoensakdi
Aran
A
Laboratory of Biochemical Products, Department of Biochemistry, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand. iaran@sc.chula.ac.th
Wangsupa
Jutakae
J
D002712:Chlorides / Q000378:metabolism; D003470:Culture Media / Q000737:chemistry; D000458:Cyanobacteria / Q000254:growth & development / Q000378:metabolism*; D005985:Glyceraldehyde / Q000378:metabolism; D007700:Kinetics; D008717:Methionine Sulfoximine / Q000378:metabolism; D009566:Nitrates / Q000037:antagonists & inhibitors / Q000378:metabolism*; D009573:Nitrites / Q000378:metabolism; D009997:Osmotic Pressure; D010710:Phosphates / Q000378:metabolism; D000644:Quaternary Ammonium Compounds / Q000378:metabolism; D012965:Sodium Chloride / Q000378:metabolism
D002712:Chlorides; D003470:Culture Media; D009566:Nitrates; D009573:Nitrites; D010710:Phosphates; D000644:Quaternary Ammonium Compounds; D008717:Methionine Sulfoximine; D005985:Glyceraldehyde; D012965:Sodium Chloride