Biomembranes energy transduction

Ho D, Chu B, Lee H, Montemagno CD (2004) Protein-driven energy transduction across polymeric biomembranes. Nanotechnology. 15(8) 1084-1094... 

However, lipid bilayers are impermeable to ions and most polar molecules, with the exception of water, so they cannot, on their own, confer the multiple dynamic processes which we see in the function of biological membranes. All of this comes from proteins, inserted into the essentially inert backbone of the phospholipid bilayer (Figure 3.27), which mediate the multiple functions which we associate with biological membranes, such as molecular recognition by receptors, transport via pumps and channels, energy transduction, enzymes, and many more. Biomembranes are noncovalent assemblies of proteins and hpids, which can best be described as a fluid matrix, in which lipid (and protein molecules) can diffuse rapidly in the plane of the membrane, but not across it. 

Pioneering work in the incorporation of functional proteins into polymer bilayers was performed by Meier et al., who integrated membrane proteins into black block copolymer membranes [250], This work proved that proteins could be incorporated into hyperthick triblock copolymer membranes while maintaining their functionality as measured by membrane conductance. Incorporation of proteins in black block copolymer films has been expanded for applications in sensors [251] and protein driven energy transduction [252] across polymeric biomembranes. 

In this chapter, we will describe as well as review briefly the work on conventional BLMs, s-BLMs, and closely related systems. As such, planar BLMs are realistic models of biomembranes they have been used to study the molecular basis of ion selectivity, membrane transport, energy transduction, electrical excitability, and redox reactions. However, one drawback with conventional BLMs is their mechanical instability. This major obstacle has now been overcome with s-BLMs which possess the requisite mechanical stability and other desired properties for biosensor development. 

Owing to complex structural and environmental factors associated with biomembranes, numerous investigators used different techniques and carried out studies on model systems in order to understand the fundamental life processes. These include ion accumulation or active transport, conduction of nerve impulses, energy transduction, protein synthesis, permeability barrier of ions and molecules, immunological reactions, phagocytosis and pinocytosis, and so on, in physical and chemical terms [3]. Under separate headings below, different model systems will be described. 

H.V.Westerhoff and K.Van Dam, Irreversible thermodynamic description of energy transduction in biomembranes, Current... 

There are many other lipid classes in this category. For instance, acyl CoA species are involved in all the cellular processes related to lipid metabolism in addition to the involvement of energy metabolism vitamins are the essential nutrients of mammals wax serves as both chemical and physical barriers for plants PA and DAG species are key intermediates for lipid biosynthesis in addition to their role in biomembrane, signal transduction, and energy metabolism as stated earlier. In summary, there is no doubt that recognition of the specific role(s) that an individual lipid class plays can clearly make the data interpretation better and insightful. 

The main principles of membrane phosphorylation are the same in chloroplasts, mitochondria, and photosynthetic bacteria. In this section, in order to analyze the role of protonmotive force in the processes of energy transduction in biomembranes, we will focus our attention on the consideration of proton-transport processes in chloroplasts. In thylakoids the ApH is the main component of transmembrane difference in electrochemical potentials of hydrogen ions, AjuH+ = Acp — 2.3(RT/F)ApH. The conductivities of the thylakoid membrane for the majority of cations (Mg ", Na ), existing... 

Mitochondria are known as the "power plants" of aerobic cells, the primary function of which is fatty acid oxidation to CO2 and H2O, and ATP synthesis. As mentioned in the INTRODUCTION, the chemiosmotic hypothesis of Mitchell suggests that coupled electron and ion movements are crucial to redox protein chain energy transduction into ATP movement. The key questions to be answered are (i) how are electrochemical potential gradients (Ap/Ax) of protons across the biomembranes generated, (ii) how are electrons, ions and chemical species transported across the membrane, and (iii) how are such potential gradients (Ap/Ax) used to drive the synthesis of ATP ... 

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