Abstract
Urate was accumulated against a concentration gradient in cells of Chlamydomonas reinhardtii by an inducible mediated transport system lacking passive diffusion and distinguishable from the urate oxidase activity. The system has a K t of 0.9 μM and an optimal pH of 6.2. Addition of ammonia to cells actively consuming urate rapidly inhibited the transport, whereas urate oxidation was not affected. Dark conditions halved urate uptake, which was not followed by a parallel decrease in urate oxidase activity. Nitrogen starvation diminished urate uptake by cells which, in contrast, exhibited high levels of urate oxidase after different periods of nitrogen deprivation. Metabolic inhibitors such as NaCN, NaN 3, 2,4-dinitrophenol and N- ethylmaleimide severely inhibited urate transport, whereas they did not appreciably affect urate oxidase in vivo. We conclude that urate uptake in C. reinhardtii is an inducible energy-dependent mediated transport process different from the enzyme-catalyzed intracellular urate oxidation.
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Schedule a callMore From: Biochimica et Biophysica Acta (BBA) - Biomembranes
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