| Abstract: | The present investigation showed that isolated cyanelles from Cyanophora paradoxa selectively enriched glutamine from the external medium, whereas glutamate poorly penetrated into these organelles. Glutamine uptake proceeded in two phases, presumably involving a low and a high affinity system. The uptake of glutamine was significantly enhanced by 2-oxoglutarate and light. Inhibitor experiments indicated that glutamine and 2-oxoglutarate were converted to glutamate by a ferredoxin-dependent glutamate synthase (GOGAT) reaction inside the cyanelles, and the glutamate formed at best slowly left these organelles. Such results were obtained independently of each other by measuring either the 14C-glutamine uptake or the 2-oxoglutarate and glutamine-dependent O2 evolution. Glutamine is suggested to be the N-compound which is supplied to the eukaryotic host. Glutamine could be exported jointly with 2-oxoglutarate, possibly employing a common carrier. Cyanelles have apparently evolved glutamine (and oxoglutarate) carrier(s) with properties not yet described for any other organism. |
