Membranes, energized state

The active transport aspect of siderophore iron utilization remains largely unexplored, although such a process probably exists—in addition to facilitated diffusion—in view of the high affinity of the cells for siderophores and the likely participation of an energized state of the membrane in their transport. Experiments with whole cells must perforce be performed with mutants lacking the ability to make these carrier molecules. 

The outer-membrane receptors exhibit two functional states. In an unenergized conformation the siderophore binds to the receptor, but is not transported through the membrane. The energized state of the receptors requires a periplasmic protein, named TonB, which serves as a coupling device between the cytoplasmic membrane and the outer-membrane receptors. It is assumed that the above mentioned... 

The atebrin/phosphorylation ratio (Table II, last column) relates inhibition of photophosphorylation to dissipation of the postulated energized state (A pH) of the thylakoid membrane. A low ratio suggests that the two responses are correlated. However, the high ratios obtained for ioxynil and propanil suggest that these two herbicides act as electron transport inhibitors rather than as uncouplers. 

The situation may be different with microorganisms, although here, too, secondary active transport of nutrients and metabolites appears to be firmly established for many transport systems. Especially the membrane bound (shock-resistant) systems which appear to be firmly incorporated in the cytoplasmic membrane are rather clearly identified as secondary active transport systems, as they require an energized state of the membrane, which means that they are driven by a proton-motive force, i.e. an electrochemical potential gradient of H -ions [3]. 

In 1992, Doring proposed using the bimetallic microcantilever stmcture to direct a fluid jet. Later, on the basis of this idea, Trah et al. [14] fabricated a micromachined normally closed valve using an Al — Si cantilever, as shown in Fig. 12. When the cantilever is in its de-energized state, the cantilever is slightly bent upward and directs the fluid to the room above the membrane. Thus, the pressure in the upper room is a little larger than that in the lower room. The pressure difference presses the boss down to the valve seat and seals the valve. When the cantilever is heated and thus bends downward, the fluid jet also deflects downward and flows into the lower room to lift up the boss. Thus, the valve opens. The size of the valve is 14.5 x 8.5 x 1.43 mm. 

Since 1970 (1), the fluorescence properties of the acridine derivatives have been utilized to detect the energization state of biological membranes. On the other hand, these compounds have been pointed out as uncoupling agents in chromatophores membranes (2,3), spinach thylakoids (4,5) and submitochondrial particles (6). However, their mechanism of action remains to be fully clarified. The results reported here are the initial part of the study of this action on thylakoid membranes of Anabaena sp. 7119. 

The membrane potential might well serve as a useful illustration of the so-called energized state of the membrane, also called a notion which is important for accounting for the bioenergetics of the transport of certain amino acids as well as for the motoric apparatus in chemotaxis. 

Notwithstanding the exciting demonstrations of the energized state in membrane vesicles, I shall here confine myself to the functions of the intact cell. 

Kraayenhof R and Arents JC (1977)Fluorescent probes for the chloroplast energized state. Energy linked change of membrane surface charge. In Roux E, ed. Electrical phenomena at the biological membrane level, pp. 493-505. Amsterdam Elsevier. 

Cytochrome 6-565 is only partially reduced by succinate in anaerobic uncoupled mitochondria and can be fully reduced by succinate in coupled mitochondria ( 2). At steady state this cytochrome is more reduced than other type 6 cytochromes and its reduction is further increased by energization of the mitochondrial membrane. Thus, cytochrome 6-565 is spectrally and functionally very similar to cytochrome 6t 16,18-20) in animal mitochondria. However, in contrast to cytochrome 6t, the En of this cytochrome is not affected by the energy state of mitochondria 22), and its a. band seems to be a single band with no appreciable shoulder even at 77°K 265). 

---