Intracellular modifications

10 Intracellular modifications following activation of various receptors (I) 

Changes in intracellular components following activation of major receptors 

Legend Increased concentration of intracellular component Decreased concentration of intracellular component cAMP cCMP Cyclic adenosine monophosphate Cyclic guanosine monophosphate 

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The intracellular modification or degradation of the substrate by metabolic sequences of enzymatic systems under aerobic conditions in connection with the respiration processes. These processes result in an increased respiratory rate. 

A permease (carrier [16]) is assumed to have the characteristics of an enzyme and thus exhibits stereospecificity for the transported solute. It can traverse the cell membrane, thus transporting the solute from the outside to the inside of the cell, and both influx and efflux of solute occur. The transport will usually exhibit saturation (Michaelis-Menten) kinetics. Enzymes involved in facilitated diffusion or active transport (i.e. permeases and molecules responsible for the intracellular modification of the transported solute) may be either constitutive or inducible. This means that the system may be present at all times (constitutive) or developed by the cell only in the presence of the transported solute (inducible). Clearly for induction to occur some of the solute must enter the cell either by way of a small (constitutive) amount of the transport system or by another means (e.g. diffusion). When the inducer concentration falls to zero or below a critical level, the transport system fails to operate thus a degree of control on the entry of the inducer is exercised. The presence of glucose in the medium may prevent the synthesis of the transport system (catabolite repression) thereby enabling glucose to be... 

Another new modification is the 2 -deoxy-2 flouro-Darabinonucleic acid (2 F-ANA), which increases the strength of the oligonucleotide-mRNA hybrids, elicits efficient RNaseH-mediated degradation of the target, is more nuclease resistant and reaches high intracellular concentrations for prolonged time. Similar results could be obtained with oxetane modified ASONs. 

Myllyharjn J (2005) Intracellular Post-Translational Modifications of CoUagens. 247 115-148... 

The Na/K ATPase has been extensively purified and characterized, and consists of a catalytic a subunit of around 95 kDa and a glycoprotein 0 subunit of approximately 45 kDa (Skou, 1992). The functional transporter exists as a dimer with each monomer consisting of an a and /3 subunit. Hiatt aal. (1984) have su ested that the non-catalytic jS subunit may be involved in the cottect insertion of the a subunit into the lipid bilayer and, therefore, it is conceivable that a modification of the 0 subunit structure may be reflected by changes in the catalytic activity of the a subunit. Therefore, in studies involving the manipulation of tissue glutathione levels, alterations of intracellular redox state may have an effect on substrate binding at an extracellular site on this ion-translocating protein. 

NOTE Following amphetamine, the intracellular postsynaptie potential (PSP) is reduced as is PI in the field potential. A reduction in the latency to and a modification in components of the rebound potential can also be observed. Time calibration 50 milliseconds. Intracellular amplitude 5 mV. 

In the x-ray structure of rhodopsin, an amphipathic helix runs parallel to the membrane from the intracellular end of TM-VII beneath the seven-helical bundle to the other side of TM-I and TM-II. At this point, one or more Cys residues are often found and are known to be subject to a dynamic posttranslational modification with palmitic acid residues. Like the phosphorylation event, the palmitoylation process appears to be dynamically regulated by receptor occupancy and is also involved in the desensitization phenomenon. The two posttranslational modifications can influence each other. For example, the conformational constraint induced by palmitoylation may alter the accessibility of certain phosphorylation sites. Like the phosphorylation process, the functional consequences of palmitoylation also appear to vary from receptor to receptor. 

As described in more detail below, agonist binding will lead to signaling as well as phosphorylation of Ser and Thr residues, especially, but also, in selected cases, Tyr residues located in intracellular loop-3 and in the C-terminal extension. This post-translational modification alters the affinity of the receptor for various intracellular proteins, including arrestin, which sterically prevents further G-protein binding and functions as an adaptor protein. Also, interaction with other types of scaffolding proteins such as PSD-95-like proteins, is influenced by the phosphorylation state of the receptor. 

For the first group (i.e. intracellular soluble enzymes and proteins), which need no posttranslational modification and complex domain organization influencing protein folding, E. coli is the most preferred choice. However, for the other targets, alternative expression systems often provide a higher rate of success. The most common expression systems are presented in this chapter. 

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