Protein cell membrane permeability

Mechanism of Action An antibiotic that alters cell membrane permeability in susceptible microorganisms. Therapeutic Effect Bactericidal activity Pharmacokinetics Negligible absorption. Protein binding low. Excreted in urine. Poor removal in hemodialysis. Half-life 6 hr. 

The absorption of labeled acetate, unlike that of glucose and pyruvate, was reduced with increasing radiation. At 1000 krads the absorption of acetate was only 1% that of the unirradiated control. This marked reduction is not to be expected on the basis of an increased acetate catabolism and reduced anabolism combined with the predicted increase in cell membrane permeability. One explanation of this anomaly could be the increased availability of acetate from within the cell itself, resulting in an increased acetate pool. Accordingly, the conversion of acetate into protein and lipids under the influence of radiation was studied. 

Heat treatment, on the other hand, elevated cytoplasmic immunoreactivity of Bcl-2. However, nuclear and mitotic Bcl-2 immunoreactivity was clearly present when these cells were fixed with formaldehyde (3.6%), followed by postfixation with methanol for 10 min at -20°C. Treatment with ice-cold methanol makes the cell membrane permeable, allowing antibody access to intranuclear antigens without protein relocalization. Extensive protein crosslinking with formaldehyde is required for maintenance of intranuclear Bcl-2 immunoreactivity. In contrast to Bcl-2, Bax immunoreactivity was detected in nuclear and cytoplasmic compartments regardless of the duration of formaldehyde fixation used. 

Since the introduction of metal-ion affinity sorbents for the fractionation of proteins [1], the method became popular for the purification of a wide variety of biomolecules. Metal-ion affinity sorbents are also widely used for the immobilization of enzymes. At present, IMAC is a powerful method for separation of phosphorylated macromolecules, particularly proteins and peptides. The significance of techniques for separation and characterization of phosphorylated biomolecules is now increasing, because phosphorylation modulates enzyme activities and mediates cell membrane permeability, molecular transport, and secretion. Phosphorylated peptides can be separated from a peptide mixture on IDA-Sepharose with Fe " ions (Fig. 2). The majority of peptides pass freely through an IMAC column, whereas acidic peptides, including phosphorylated ones, are retained and can be released by a pH gradient. 

Calyculins A-H are bioactive metabolites isolated from the sponge Discodermia calyx Calyculins are potent serine-threonine protein phosphatase (PPl and PP2A) inhibitors and endowed with remarkable cell membrane permeability. The absolute stereochemistry of calyculins and its C33—C37 portion has been investigated. The relative configuration of the stereocenters was determined by X-ray analysis. ... 

Cell membrane The cell membrane is composed of about 45% lipid and 55% protein. The lipids form a bilayer that is a continuous nonpolar hydrophobic phase in which the proteins are embedded. The cell membrane is a highly selective permeability barrier that controls the entry of most substances into the cell. Important enzymes in the generation of cellular energy are located in the membrane. 

TBT and TFT are membrane-active molecules, and their mechanism of action appears to be strongly dependent on organotin(IV) lipophilicity. They function as ionophores and produce hemolysis, release Ca(II) from sarcoplasmic reticulum, alter phosphatodylseiine-induced histamine release, alter mitochondrial membrane permeability and perturb membrane enzymes. Organotin(IV) compounds have been shown to affect cell signaling they activate protein kinase and increase free arachidonic acid through the activation of phospholipase... 

The actions of proteins isolated from sea anemones, or other coelenterates, involve mechanisms different from those described for saponins. Thus, hemolysins from sea anemone R macrodactylus are capable of forming ion channels directly in membranes (98). The basic protein from S. helianthus also forms channels in black-lipid membranes. These channels are permeable to cations and show rectification (99). This ability of S. helianthus toxin III to form channels depends upon the nature of the host lipid membrane (100). Cytolysin S. helianthus binds to sphingomyelin and this substance may well serve as the binding site in cell membranes (101-106). 

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