Taxi mechanism

Palmitoylcoprogen (Table 2 last entry) from Trichoderma spp. is retained in the fungal mycelium and may therefore be considered as a candidate for an iron uptake taxi mechanism (5). 

Iron transport was studied using the Fe " - and H-complexes of parabactin (25). After a quick uptake of 10% of both labels there was a continuing steady uptake of Fe " while the amount of remained constant. This could either mean that after binding to the cell surface Fe only is transferred into the cell ( taxi mechanism ) or there is a fast re-export of the ligand. A decision in favor of the... 

The schizokinen-mediated Fe " transport in Bacillus megaterium was studied by double labelling with e and (8). At 37°C, uptake of Fe and of are parallel during the first 30 sec, then that of e continues until it levels off after 2 min, while that of [ H]-schizokinen drops to a low constant level. At 0°C, uptake of both labels reaches this low level which is obviously due to the binding of the ferri-siderophore to the cell surface. At 37°C, transport into the cell, release of iron, and re-export of the ligand follow. Apparently a shuttle mechanism takes place, cf. the experimental results obtained with parabactin (Sect. 3.2) indicative of a taxi mechanism. 

Phototaxis has been examined in some detail in a number of photosynthetic prokaryotes (9), particularly halophilic Archaea, purple photosynthetic Proteobacteria, and Cyanobacteria (for purple bacteria and Archaea, see Fig. 1). Two very different mechanisms of photosensing are at the basis of these photo taxis responses some responses are triggered via light absorption by the photosynthetic machinery, while others involve dedicated photosensory proteins. 

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