Subject membrane binding

Recent evidence indicates that the 5-HT transporter is subject to post-translational regulatory changes in much the same way as neurotransmitter receptors (Blakeley et al. 1998). Protein kinase A and protein kinase C (PKC), at least, are known to be involved in this process. Phosphorylation of the transporter by PKC reduces the Fmax for 5-HT uptake and leads to sequestration of the transporter into the cell, suggesting that this enzyme has a key role in its intracellular trafficking. Since this phosphorylation is reduced when substrates that are themselves transported across the membrane bind to the transporter (e.g. 5-HT and fi -amphetamine), it seems that the transport of 5-HT is itself linked with the phosphorylation process. Possibly, this process serves as a homeostatic mechanism which ensures that the supply of functional transporters matches the demand for transmitter uptake. By contrast, ligands that are not transported (e.g. cocaine and the selective serotonin reuptake inhibitors (SSRIs)) prevent the inhibition of phosphorylation by transported ligands. Thus, such inhibitors would reduce 5-HT uptake both by their direct inhibition of the transporter and by disinhibition of its phosphorylation (Ramamoorthy and Blakely 1999). 

Substituted benzamides with a bulky quinolizidine moiety, such as Q11, were subjected to binding assays to 5-HT3 and D2 receptors on membranes obtained from bovine area postrema ([ H]-GR65630) and rat striatum... 

Insulin receptors. Iti.suLin receptors are membrane-spanning glyco-proieins consisting of two a-siibimits and two fl-subunits linked cova-Icnily by disulphide bonds. After insulin binds to the u-subuntt. the insulin-receptor complex enters the cell, where the insulin is destroyed hy lysosomal enzymes. The internalization of the insulin-receptor complex underlies the (iown-re)(ulan(jii of receptors that is produced hy high levels of insulin (e.g. in obese subjects). The binding of insulin to the receptors activate.s the tyrosine kinase activity of the p-subunii and initiates a complex chain of reactions that lead to the effecLs of insulin. 

For the prolis to survive a filtration without losing their content, the temperature is lowered below the phase change point of the phospholipids being used. The filtration procedure resembles those for membrane binding assays (see Section 2.2.3). However, they are different insofar as you need to keep an eye on the stability and tightness of the compartments (and perhaps on ion gradients between compartment and media). The compartments must not be subjected to osmotic stress. 

More than 50 proteins have been discovered in the cytosol of nonmuscle cells that bind to actin and affect the assembly and disassembly of actin filaments or the cross-linking of actin filaments with each other, with other filamentous components of the cytoskeleton, or with the plasma membrane. Collectively, these are known as actin-binding proteins (ABPs). Their mechanisms of actions are complex and are subject to regulation by specific binding affinities to actin and other molecules, cooperation or competition with other ABPs, local changes in the concentrations of ions in the cytosol, and physical forces (Way and Weeds, 1990). Classifications of ABPs have been proposed that are based on their site of binding to actin and on their molecular structure and function (Pollard and Cooper, 1986 Herrmann, 1989 Pollard et al., 1994). These include the following ... 

Inhibition of the lipid modification cascade provides an alternative way to block aberrant signaling pathways and that opportunity can be exploited in anticancer therapy. As part of the growth factor, signaling of the false activation is transmitted by the mutated ras gene encoded proteins (Ras) and ultimately leads to uncontrolled cell growth. These typical GTP binding proteins are also subject to membrane anchoring and the biosynthesis of those Ras proteins can be blocked at the posttranslational prenylation step. 

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