Nitrite transport activity of the ABC-type cyanate transporter of the cyanobacterium Synechococcus elongatus.
In addition to the ATP-binding cassette (ABC)-type nitrate/nitrite-bispecific transporter, which has a high affinity for both substrates (K(m), approximately 1 microM), Synechococcus elongatus has an active nitrite transport system with an apparent K(m) (NO(2)(-)) value of 20 microM. We found that this activity depends on the cynABD genes, which encode a putative cyanate (NCO(-)) ABC-type transporter. Accordingly, nitrite transport by CynABD was competitively inhibited by NCO(-) with a K(i) value of 0.025 microM. The transporter was induced under conditions of nitrogen deficiency, and the induced cells showed a V(max) value of 11 to 13 micromol/mg of chlorophyll per h for cyanate or nitrite, which could supply approximately 30% of the amount of nitrogen required for optimum growth. Its relative specificity for the substrates and regulation at transcriptional and posttranslational levels suggested that the physiological role of the bispecific cyanate/nitrite transporter in S. elongatus is to allow nitrogen-deficient cells to assimilate low concentrations of cyanate in the medium. Its contribution to nitrite assimilation was significant in a mutant lacking the ABC-type nitrate/nitrite transporter, suggesting a possible role for CynABD in nitrite assimilation by cyanobacterial species that lack another high-affinity mechanism(s) for nitrite transport.
Maeda
Shin-ichi
S
Laboratory of Molecular Plant Physiology, Graduate School of Bioagricultural Sciences, Nagoya University, Nagoya 464-8601, Japan. maeda@agr.nagoya-u.ac.jp
Omata
Tatsuo
T
D027321:Anion Transport Proteins / Q000235:genetics / Q000378:metabolism*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D001692:Biological Transport / Q000235:genetics; D003485:Cyanates / Q000378:metabolism*; D016254:Mutagenesis, Insertional; D009573:Nitrites / Q000378:metabolism*; D046940:Synechococcus / Q000235:genetics / Q000378:metabolism*
D027321:Anion Transport Proteins; D001426:Bacterial Proteins; D003485:Cyanates; D009573:Nitrites