Proteins shifts

One should note overall, that while some of these suggested mechanisms may in the future prove to have a role in the control of smooth muscle contraction, in chemically skinned preparations maximum force development follows activation by the MLCK active subunit in extremely low Ca " ion concentrations. The conclusion can hardly be avoided that phosphorylation alone is sufficient for activation, and if another mechanism is involved, it is not necessary for the initial genesis of force. If such mechanisms are operative, then they might be expected to run in parallel or consequent to myosin phosphorylation. A possible example of this category of effect is that a GTP-dependent process (G-protein) shifts the force vs. Ca ion concentration relationship to lower Ca ion concentrations. This kind of mechanism calls attention to the divergence of signals along the intracellular control pathways. 

The fluid and protein shift into the abdomen (called third-spacing) may be so dramatic that circulating blood volume is decreased, which causes decreased cardiac output and hypovolemic shock. Accompanying fever, vomiting, or diarrhea may worsen the fluid imbalance. A reflex sympathetic response, manifested by sweating, tachycardia, and vasoconstriction, may be evident. With an inflamed peritoneum, bacteria and endotoxins are absorbed easily into the bloodstream (translocation), and this may result in septic shock. Other foreign substances present in the peritoneal cavity potentiate peritonitis, notably feces, dead tissues, barium, mucus, bile, and blood. 

When bacteria become dispersed throughout the peritoneum, the inflammatory process involves the majority of the peritoneal lining. Fluid and protein shift into the abdomen (called third spacing ) may decrease circulating blood volume and cause shock. 

PI precipitation is suitable for a protein with very low solubility and is more effective in combination with salting-out and organic solvent precipitation. Anions bind with proteins more easily than cations, so the PI of proteins shifts a little to the acidic range. 

Heteroallostery - This type of allosteric control involves heteroallosteric effectors which may be either inhibitors or activators of binding. If an enzyme can exist in two conformational states, T and R, that differ dramatically in the strength with which substrate is bound or which differ significantly in the catalytic rate, then the kinetics of the enzyme can be controlled by any other substance that, in binding to the protein, shifts the T<=>R equilibrium. Allosteric inhibitors shift the equilibrium toward T and activators shift it toward the R state. 

It is now believed that perilipin guards the fat resources of the lipid droplet. When not phosphorylated, the protein does not allow fat-digesting enzymes access to the triacylglycerols. When phosphorylated, the protein shifts conformation and allows access. Studies with mutant mice lacking perilipin have shown that such mice eat much more than their wild-type counterparts, yet burn off two-thirds of the extra calories consumed. The figure shows three different strains of mice. The mouse on the left is normal. The mouse on the right is an obese mouse from a strain that lacks the ability to respond to an appetite suppressing hormone called leptin. The mouse in the middle is a double... 

Seet BT, McCaughan CA. Handel TM et al. Analysis of an orf virus chemokine-binding protein shifting ligand specificities among a family of poxvirus viroceptors. Proc Natl Acad Sci USA 2003 100(25) 15137-15142. 

Assodation of enzyme proteins shift of balance between de novo enzyme synthesis and enzyme degradation by gronp-spedfic proteases (inactivases). Enzyme concentration... 

In the titration curves of lysozyme in the presence of ovalbumin, ovalbumin only weakly interfered with the complexation of lysozyme and PAA. However, in the egg white system, only 3.4% of the protein is lysozyme. Most of the proteins have net charges opposite to that of lysozyme below the isoelectric point of lysozyme, pH 10.7. The likelihood of interactions among the proteins shifting the critical pH is much greater Fig. 16.8 shows this to occur for all but the highest MW. Why the critical pH of MW 4000000 PAA was not much affected (compare Figs. 16.6 and 16.8) is not understood. However, the absence of a shift is an indication of selective removal of the lysozyme such behavior is desirable in trying to fractionate proteins by precipitation. 

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