Membranes fluidity affecting

At physiological pH in plants, polyamines exist as proton-ated forms. These protonated forms bind to the negatively charged phospholipid head groups and other anionic sites in membranes and alter the stability and permeability characteristics of such membranes. Polyamines also stabilize chloro-plast thylakoid membranes and retard chlorophyll loss in senescing barley leaf tissue. Polyamines also influence membrane fluidity, affect membrane localized proton pumps, and alter plant hormone responses, perhaps by competing for... 

Thalhammer T, Kaschnitz R, Mittermayer K, et al. 1993. Organic solvents increase membrane fluidity and affect bile flow and K+ transport in rat liver. Biochem Pharmacol 46(7) 1207-1215. 

The answer is E. Anesthetics are highly lipid-soluble and experiments with isolated membranes indicate that these molecules can dissolve in the hydrophobic center of the membrane bilayer. This causes a measurable increase in the membrane fluidity by disrupting the packed structure of phospholipids tails. This is considered to be the main, direct mechanism by which this class of drugs inhibits neurotransmission (pain sensations) in neurons. Hallucinogens and opiates may also affect membrane fluidity, but their effects occur by indirect mechanisms, resulting from changes in the protein or lipid composition of the membranes. 

Inhibitors of HMG-CoA reductase activity (for example compac-tin240), or compounds that lower the levels of the enzyme (including a number of oxygenated cholesterol derivatives,241- 24 la such as 25-liy-droxycholesterol), not only decrease the formation of polyprenyl diphosphate, but also affect the formation of cholesterol and the polyprenyl side-chains of coenzyme Q. Consequently, prolonged treatment with such compounds may cause side effects, for example, changes in membrane fluidity (see also, Section III,5), decreased activity of membrane enzymes,1214,2,3 and inactivation of membrane transport systems,246 and, therefore, indirectly prevent glvcosvlation of proteins. 

Lipid-free (Na+, K+)-ATPase is incapable of hydrolyzing ATP or p-nitrophenyl phosphate. The precise role of the lipid and the specificity for the lipid have not yet been determined. The addition of lipid to the delipidated enzyme brings about conformational changes, with phosphatase activity regenerated before ATPase activity.51 It seems evident that the lipid will affect the conformation of the enzyme and determine membrane fluidity, which is relevant to conformational change. 

Membrane effects. Drugs may alter synaptic transmission by affecting membrane organization and fluidity. Membrane fluidity is basically... 

Awayda et al. [278] suggested that CPZ-induced alteration of epithelial sodium channels (ENaC) could be a result of the influence exerted by the phe-niothiazine derivative on the membrane fluidity. To demonstrate it they used epithelial sodium channels expressed in Xenopus laevis oocytes as a model, and compared the effects of CPZ (9) and temperature on the ENaC activity. They have shown that a decrease of membrane order caused either by the increase of temperature or by incorporation of drug molecules into the membrane affected the conductance of epithelial sodium channels in a very... 

With regard to its effect on neurotransmitter function, alcohol increases adenylate cyclase activity, possibly via the membrane-bound G protein complex. The effect of alcohol on the secondary messenger system appears to depend on its location the noradrenaline-linked cyclase in the cortex seems to be directly affected by the drug, whereas the dopamine-linked enzyme in the basal ganglia appears to be altered by a combination of changes in the membrane fluidity, together with those in the G protein-cyclase complex. 

Cholesterol - an essential component of mammalian cells - is important for the fluidity of membranes. With a single hydroxy group, cholesterol is only weakly am-phipathic. This can lead to its specific orientation within the phospholipid structure. Its influence on membrane fluidity has been studied most extensively in erythrocytes. It was found that increasing the cholesterol content restricts molecular motion in the hydrophobic portion of the membrane lipid bilayer. As the cholesterol content of membranes changes with age, this may affect drug transport and hence drug treatment. In lipid bilayers, there is an upper limit to the amount of cholesterol that can be taken up. The solubility limit has been determined by X-ray diffraction and is... 

MI-D (42) reduced the rate of swelling induced by valinomycin-K+, as well as induced swelling in the presence of nigericin-K+. Shrinkage was also affected, suggesting interference with the inner mitochondrial membrane, which would affect both the fluidity and elasticity. These alterations in the membrane fluidity are thus related to the effect of MI-D on the energy-linked functions of mitochondria [80]. 

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