Solubilization membrane, interactions with

One inherent property of peptides that interact with membranes is that self-association or even aggregation will interfere with solubilization by organic solvents or micelles. The preparation, purification and sample preparation of extremely hydrophobic (often transmembrane) peptides is nontrivial and has been addressed by only a few papers [74—79]. 

I didn t use the triton X-100 example because it is a neutral entity. It is fine for an organic chemist, but inorganic entities can t interact with this micelle. However, a triton X-100 micelle is very well studied because biochemists are interested in using it as a model membrane since it makes big flat-disk micelles. Biochemists consider it as resembling a section of membrane, which can solubilize proteins. It is a good model for biological systems. 

Fig. 11. A pictorial representation of the mitochondrial ATP synthesizing coupling factor interacting with the mitochondrial membrane. F, contains five polypeptide chains a, (3, 7, 8, and e and is readily solubilized. The stalk is probably made up of three polypeptide chains, 8, OSCP, and Ffi, which interact with a small group of hydrophobic polypeptides, CF0, embedded in the membrane.

A number of cases are known in which the properties of an enzyme are markedly altered by interaction with a membrane. Of course, in some cases the normal function of an enzyme is destroyed when it is removed from the membrane. For example, the mitochondrial coupling factor cannot synthesize ATP when removed from the membrane, since coupling to a proton gradient is required. The portion of the coupling factor that is easily solubilized (F,) is an ATPase. The steady-state kinetic properties of this solubilized ATPase are appreciably changed when it is reconstituted with mitochondrial membranes The turnover numbers and pH dependencies are different the solubilized enzyme is strongly inhibited by ADP, whereas the reconstituted enzyme is not and the reconstituted enzyme is inhibited by oligomycin, whereas the solubilized enzyme is not. 

The sample is disrupted completely and distributed over the surface as a function of interactions with the support, the bonded phase, and the tissue matrix components themselves. The solid support acts as an abrasive that promotes sample disruption, whereas the bonded phase acts as a lipophilic, bound solvent that assists in sample disruption and lysis of cell membranes. The MSPD process disrupts cell membranes through solubilization of the component phospholipids and cholesterol into the Cis polymer matrix, with more polar substituents directed outward, perhaps forming a hydrophilic outer surface on the bead. Thus, the process could be viewed as essentially turning the cells inside out and forming an inverted membrane with the polymer bound to the solid support. This process would create a pseudo-ion exchange-reversed-phase for the separation of added components. Therefore, the Cis polymer would be modified by cell membrane phospholipids, interstitial fluid components, intracellular components and cholesterol, and would possess elution properties that would be dependent on the tissue used, the ratio of Cis to tissue employed and the elution profile performed (99-104). 

Surfactants act as solubilizers, stabilizers, emulsiLers, and wetting agents. They can also causi toxicity and disrupt normal membrane structure. Surfactant toxicity is directly related to its concentration. This should be considered by the pharmaceutical formulator so levels below the toxic concentration will be used for a particular application. Many of the toxic effects of the surfactants are related to their physicochemical properties and their interaction with biological membranes and other macromolecular assemblies. The observed protein binding and lipid solubilization is directly... 

As indicated earlier, the intent of this section was not to be global with respect to the scope of its coverage, but rather to discuss in general terms some considerations common to the study of ligands which interact with membrane receptors and, thereby, elicit post-binding events. Many of the examples chosen have been drawn from my experience with the follitropin-gonadal receptor system, but they provide instances of problems, concerns and caveats in use of techniques and interpretation of results that are common to this particular field of study. The reader is referred to the specific examples of hormone receptor interactions to follow, wherein aspects of the problems not germaine to this section, such as, for example, techniques for purification of solubilized receptors, are considered in detail. 

The components in a simple penetration experiment consist of a surfactant, water-soluble herbicide, and water. Since the surfactant is at a concentration of 0.5 to 1%, it interacts with water and forms micelles. Since micelles are formed, these could solubilize some of the herbicide inside the micelle. Now we have five components, (1) water, (2) surfactant monomer, (3) surfactant micelle, (4) micelle with solubilized herbicide, and (5) an herbicide in anhydrous or hydrated form which all come in contact with the plant. Which one or more of these components has the greatest effect on the plant Before a thorough understanding of this phenomenon can be achieved, the interaction of each of these components with a plant must be investigated separately, and perhaps the plant is too complex for initial study. Perhaps a homogeneous semipermeable membrane could be used instead. 

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