1,721,141 research outputs found
Short-term regulation of nitrate uptake by a 'pump and leak' mechanism in the acidophilic nonvacuolated alga, Cyanidium caldarium
No full textIn the nonvacuolated acidophilic thermophilic red alga, Cyanidium caldarium, nitrate uptake and reduction can be separated by measuring disappearance of nitrate from the suspension medium using, in in vivo experiments, cyanate, a competitive inhibitor of algal nitrate reductase. Cyanate selectively inhibited nitrate reduction at concentrations that did not significantly affect nitrate uptake, photosynthesis or respiration. Its use proved that short-term control of intracellular nitrate through the increase of a carrier-mediated nitrate efflux took place when nitrate reduction was inhibited. The occurrence of the high- and low-affinity nitrate uptake systems in cells grown in nitrogen-limited conditions, as previously reported, suggests a 'pump and leak' mechanism operating at the plasmalemma level to regulate nitrate uptake and intracellular nitrate: the high-affinity nitrate transport system mediated by proton cotransport (irreversible) operates the influx, while the low-affinity transport (reversible) operates influx or efflux according to cell requirements. Kinetic analysis of cyanate inhibition in cells taken from low-nitrate medium supports this hypothesis and reveals that, in Cyanidium, intracellular nitrate is probably compartmented in the cytosol. © 1989 Elsevier Science Publishers B.V. (Biomedical Division)
Mechanism of proton-linked nitrate uptake in Cyanidium caldarium, an acidophilic non-vacuolated alga
No full textThe unicellular non-vacuolated alga Cyanidium caldarium, grown under conditions of nitrogen limitation, possesses two permease systems for nitrate uptake, one of which, the so-called 'high-affinity nitrate uptake system', enables the alga to take up nitrate through a mechanism involving cotransport of protons. Measurements of nitrate and proton stoichiometry, and determination of the kinetic parameters of uptake in cells resuspended in medium adjusted at different pH values, are consistent with a mechanism of uptake in which two protons for each nitrate ion are transported across the plasmalemma. Furthermore, kinetic data suggest that the carrier first binds nitrate and, subsequently, protons. Permutations of this binding sequence do not agree with the experimental results. © 1985
Competition between nitrate and nitrite as a tool to study regulation by ammonium of nitrate metabolism in the microalga Cyanidium caldarium.
No full textThe strong inhibition by nitrate of nitrite utilization in the acidophilic alga Cyanidium caldarium indicated that nitrite uptake could also occur through the high affinity nitrate uptake system, besides the free diffusion of HNO2. In the presence of ammonium, which inhibited nitrite assimilation, nitrite transport through the high affinity nitrate uptake carrier was not affected
UPTAKE AND ASSIMILATION OF NITRITE IN THE ACIDOPHILIC RED ALGA CYANIDIUM-CALDARIUM GEITLER
No full textThe acidophilic red alga, Cyanidium caldarium Geitler, could use nitrite as a nitrogen source for growth, although this compound was very toxic in acidic media. Growth could be sustained when nitrite was added continuously at a rate lower than the maximum rate of nitrite assimilation for the culture. Nitrite assimilation was derepressed in cells growing on nitrate or nitrite, under nitrogen limitation and by nitrogen starvation. Ammonium‐grown cells showed a limited capacity for nitrite reduction in the light, even if nitrite reductase was not detectable in cell extracts. In acidic media nitrite was taken up mainly through HNO, influx. Nitrite assimilation, in viva, was restricted by a saturable step under conditions in which nitrite uptake was not limiting. The pH of the cell suspension affected nitrite assimilation by changing the K1⁄2 over the pH range tested but not the Vmax. The K1⁄2 was inversely proportional to the concentration of H+ in the medium. The apparent Km value for nitrite of nitrite reductase, in vitro, and its expected apparent Km value, in vivo, estimated from the K1⁄2 of nitrite assimilation, suggested that the activity of this enzyme may not be the limiting step of nitrite assimilation. Copyright © 1993, Wiley Blackwell. All rights reserve
Cytoskeletal elements in the liverworts “lunularia cruciata “ and “ conocephalum conicum “ revealed by sem
No full text- …
