Transport of Solutes Across Biological Membranes: Prokaryotes

Critical Evaluation of Physicochemical Parameters and Processes for Modelling the Biological Uptake of Trace Metals in Environmental (Aquatic) Systems

“…In most cases, a receptor or carrier protein must convey information to the cell interior to indicate that binding has taken place, resulting in the initiation of a number of processes including: catalysis, signal and energy transduction, cross-membrane transport and cellular defence mechanisms [114]. Because microorganisms do not have specific transport systems for the vast majority of compounds that are internalised by the cell, most compounds must borrow existing pathways designed for the essential elements: transport through ion channels, carrier-mediated transport, active transport and endocytosis [24,242]. In addition, passive diffusion through the cell membrane (hydrophobic compounds, e.g.…”

“…In contrast, soft metals are often toxic, due to their ability to replace transition metals in biological structures. These and other biological mechanisms of the internalisation process have been discussed in much greater detail in Chapters 6 and 7 of this volume [24,245] and elsewhere (e.g. [242,246,247]).…”

“…Na þ , Ca 2þ , Zn 2þ , some sugars and amino acids) can be concentrated in the cell against their electrochemical gradient (active transport systems), the kinetic implications of an active transport mechanism will be examined in Section 6.1.3. Further explanations of the mechanisms themselves can be obtained in Chapters 6 and 7 of this volume [24,245].…”

“…Under iron-limiting conditions, many organisms are known to release siderophores that strongly complex and solubilise iron (see Chapter 6 of this volume; [24]). Internalisation of the iron chelates occurs by specific membrane transport proteins [259,[320][321][322] followed by the recovery of the iron inside the cell via metal reduction or siderophore degradation reactions [320,323].…”

“…On the other hand, for sufficiently high densities of microorganism, siderophore concentrations may accumulate to the point where transport is increased. This specific example of biological modification of cellular transport was examined in much greater detail in Chapter 6 of this volume [24].…”