Translocation Subject

Methods used to demonstrate the existence of membrane phospholipid asymmetry, such as chemical labelling and susceptibility to hydrolysis or modification by phospholipases and other enzymes, are rmsuitable for dynamic studies because the rates of chemical and biochemical reactions are of a different order compared to the transmembrane translocahon of the phospholipids. Indirect methods have therefore been developed to measure the translocation rate which are consequent on the loss of membrane phospholipid asymmetry. Thus time scales appropriate to rates of lipid scrambling under resting conditions or when the forces preserving the asymmetric phospholipid distribution are disturbed can be monitored. Generally the methods rely on detecting the appearance of phosphatidylserine on the surface of cells. Methods of demonstrating Upid translocation in mammalian cells has been the subject of a recent review (Bevers etal., 1999). 

Binding of phosducin to the Pycomplex leads to its translocation from the membrane into the cytosol. In this way, the number of Py-complexes available for the G-protein cycle is reduced and signal transmission is weakened. Interestingly, the phosdu-cin function is subject to regulation by phosphorylation. In the Ser-phosphorylated form, binding to the Py-complex is greatly weakened. 

Fig. 12.2. Model of Notch signalling. The Notch protein is a ligand activated transmembrane receptor which is subject to proteolysis of the intracellular domain upon ligand binding. The nature of the protease involved is still a matter of debate. The proteolytically released intranceUu-lar domain of Notch (NICD) translocates into the nucleus where it interacts with a family of transcription factors, the CSL proteins, resulting in a change in transcription of target genes.

CGA 245704 (acibenzolar Figure 4.39) may operate in a similar manner to natural defence activators. It does not possess fungicidal activity per se but induces resistance to a wide range of pathogens. The product is readily translocated in the phloem and xylem but is subject to rapid metabolism. 

In the biosphere, vanadium can be considered to be of two forms, one of which is highly mobile, whereas the other is a virtually immobile form. These are closely connected to the oxidation state of vanadium, where the mobile chemically reactive form conforms more or less, but certainly not exclusively, to the V(V) oxidation state. This is the state that vanadium will predominantly have in gas effluents in ash from oil, coal, and gas burners in some minerals and in surface water. Vana-dium(IV) complexes of the types found in minerals will often be relatively immobile but, if subjected to an oxidative environment, can enter the mobile phase in the V(V) oxidation state. Sequestered forms of vanadium can be transported by mechanical processes such as by movements of suspended materials in creeks and rivers, where translocation from terrestrial to lake or marine environments accounts for a high percentage of the movement of vanadium. This procedure does not release the vanadium into the environment in the sense that release from the substrate does rather, the vanadium is simply redeposited as the sediments settle. However, because of the high surface area of the suspended materials, vanadium can efficiently be removed from the suspended material by chemical reactions and enter into the environment as active species by this process. 

Fig. 1. Densitometry analysis of coimmunoprecipitation studies of NF-reB dimers in nuclear extracts of primary cortical neurons exposed to OGD or cortices from mice subjected to MCAO. Either OGD or MCAO induces nuclear translocation of p50/RelA dimers. The nuclear content of RelA/c-Rel complexes decreased while p50/c-Rel remained unchanged. Data are expressed as ratio of OGD to controls or ratio of MCAO to contralateral cortex. Values are expressed as means S.E.M. ( p < 0.05 vs. the corresponding control value). For methods and details, see Sarnico et al. (2009).

Since oxidative stress has been reported to produce subcellular redistribution and activation of NF-kB, we measured total NF-kB content in cytosolic and particulate fractions of the hearts subjected to ischemia/reperfusion. In another set of experiments, the activation of NF-kB protein was studied by measuring the total NF-kB and phospho-NF-KB in the heart homogenate. Elevated ratios of NF-kB in particulate versus cytosolic fraction and of phospho-NF-KB and total NF-kB in the hearts subjected to ischemia/reperfusion were reduced by selenium. As oxidative stress has been reported to produce subcellular redistribution and activation of NF-kB and antioxidants have been shown to prevent this alteration (Cargnoni et al. 2002), it is possible that our observation on selenium-induced NF-kB translocation might be due to its antioxidant action. It should be noted that since selenium treatment could reduce the tumor necrosis factor-cc (TNF-ct)-mediated activation of NF-kB (Kim and Stadtman 1997), it suggests a possible involvement of a reduction in the formation of TNF-tx in the hearts subjected to ischemia/reperfusion by selenium. 

This test is usually much more sensitive, but considerably more expensive and slower, than the dominant-lethal test,131 and it deals with a clearly defined type of mutation that is transmitted to and scored in viable offspring. Males are exposed to the test substance and mated to untreated females. Male progeny (usually derived only from post-sperroatogonial treatments) are tested for translocations by the fertility test or the cytogenetic test. In the fertility test, males are tested, usually with a sequential procedure, to determine fertility rates.137 Animals suspected of having a translocation (because of decreased fertility) are then subjected to cytologic examination. 

Isolated keratinocytes subjected to cyclic strain exhibit a significant increase in cell proliferation, DNA synthesis, and protein synthesis compared to stationary or constantly loaded cells, which appear to involve changes in cyclic AMP. Takei et al. (1997) reported a strain-induced reduction in the levels of cyclic adenosine monophosphate, protein kinase A (PKA), and prostaglandin E2 (PGE2) as compared to stationary controls. Takei et al. (1997) also studied the effects of cyclic strain on protein kinase C (PKC) activation and translocation in cultured keratinocytes. 

The word "aspects is intentionally used in the title of this book because of the broadness it allows in the subject matter. It allows a discussion of principles such as in Chapter 20. Here the principles have been established, and reference has been made to their possible utilization in determining the critical surface tension of an insect. Perhaps this paper will stimulate workers to do obvious research which could yield data explaining the specificity in control of various insects. The word aspects also allows a discussion of the direct use of these physicochemical principles to solve formulation problems such as the paper by Freed and Witt on the translocation of herbicides in plants. Thirdly, this symposium contains papers dealing with phenomena that clearly are physical and colloidal but which have not as yet been the subject of rigorous physical chemical studies. For example, in Lyon s paper the effect of varying crystal size is shown to be very important in controlling... 

Some indirect method of measuring evaporative loss is needed because of the difficulty of direct measurements. Total amounts in random crop samples at various times after spraying can be measured by residue analytical methods (radioactive tracer or otherwise). The rate of loss so determined is subject to large statistical errors and includes losses by chemical and biochemical reaction and perhaps translocation in the crop as well. Exposure of typical test surfaces treated with some model substance, preferably less volatile than water but sufficiently volatile for simple gravimetric procedure, would seem the most suitable. We will see, however, how successful water is as a model for providing rough estimates. 

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