Transport ionophore-mediated

Painter, G. R., Pressman, B. C. Dynamic Aspects of Ionophore Mediated Membrane Transport, ibid., p. 83M10... 

Dynamic aspects of ionophore mediated membrane transport. G. R. Painter and B. C. Pressman, Top. Curr. Chem., 1982,101, 83-110 (105). 

Ionophore-mediated ion transport (down electrochemical gradient)... 

Alkali metal transport in biochemistry is a vital process in maintenance of cell membrane potentials of use, for example, in nerve signal transduction and is at the core of some of the early work on artificial ionophores that mimic natural ion carriers such as valinomycin. Ionophore mediated ion transport is much slower than transport through cation and anion ion channel proteins, however. 

Be familiar with the composition and structure of biologic membranes. Be able to place the various phospholipids in the membrane bilayer. Know the function and position of membrane proteins and their possible movements. Know how membrane fluidity is controlled. Know the nature of various mechanisms to transport substances across membranes, receptor-mediated endocytosis, active and facilitated transport, ionophores, and the various types of channels. Be able to solve simple mathematical problems by creating solute gradients across membranes. Know the names of substances that inhibit the various modes of transport across membranes. 

The test is based on an ion-selective reaction. The reaction takes place in a cellulose matrix into which an organic phase and the substances of the aqueous phase have been incorporated. If a sample is applied, the aqueous phase reconstitutes itself. The potassium-selective ionophore mediates the transport of the potassium ion from the aqueous phase to the organic phase. The neutrality of charge of the organic phase is ensured by the simultaneous loss of a proton by the indicator dye. The release of a proton results in a change of the absorption of the dye that can be measured at 640 nm at intervals of 5 seconds by measuring the reflectance. The result is displayed after 45 seconds. 

Figure 2. Different modes of ionophore-mediated transmembrane transport. Neutral ionophore-mediated transport is depicted on the left and carboxylic ionophore-mediated transport, on the right. The individual transport steps are detailed in...

Because of the greater flexibility imparted them by the lack of head-to-tail covalent linkage, the carboxylic ionophores respond much more strongly to environmental forces such as local polarity than do the neutral macrocyclic ionophores. Upon leaving a membrane interface during the course of a catalytic transport cycle, an ionophore does not experience an abrupt change from a polar aqueous environment to an apolar hydrocarbon-like environment. The polarity boundary is rather diffuse. In order to properly evaluate the factors affecting carboxylic ionophore mediated transport, it is necessary to determine the effects of each of the microenvironments encountered within the membrane on the conformation of the ionophore and the stability of the ionophore-ion inclusion complex. 

The recognition that the strictly monovalent ionophores produce cardiovascular effects in animals similar to those produced by lasalocid indicates that the a priori rationale implicating direct Ca transport by ionophores to be naive > . This conclusion is reinforced by the observation that A23187, the most specific Ca transporter, produces relatively week cardiovascular effects in intact animals It appears that the common denominator for cardiovascular responses is ionophore mediated Na and transport rather than direct transport of Ca and/or catecholamines ... 

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