Characteristics of the uptake system for L-lysine and L-arginine inPhaeodactylum tricornutum |
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Authors: | K J Flynn P J Syrett |
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Institution: | (1) Plant and Microbial Metabolism Research Group, School of Biological Sciences, University College of Swansea, Singleton Park, SA2 8PP Swansea, South Wales, UK |
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Abstract: | Cells ofPhaeodactylum tricornutum Bohlin develop the ability to take up L-lysine when they are deprived of nitrogen (illuminated in nitrogen-free medium), carbon (incubated in darkness) or both. Cells with a developed uptake system take up and accumulate lysine in an unchanged form. Uptake occurs under either aerobic or anaerobic conditions and is dependent on the presence of sodium+ ions (K
s
Na
+=,ca. 10 mM). Some potassium+ ions are necessary for uptake, presumably within the cells, but with potassium+-replete cells, increasing K+ concentration depresses lysine uptake. The lysine-uptake porter also transports L-arginine.K
s values are about 1.5 M for lysine and 0.5 M for arginine. It is, however, possible that the uptake system developed by incubating cells in darkness differs from that produced in light; it shows a pronounced pH optimum at pH 8.5, whereas the activity of the light-developed system declines from pH 6.5 to pH 9.0 and correlates well with the concentration of lysine+. The uptake system developed in darkness may also have a higher affinity for lysine. Lysine uptake is not inhibited by 1 mM concentrations of nitrate, nitrate, ammonium, or urea nor by similar concentrations of amphoteric or acidic amino acids. |
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