Enzyme and membranes

N. C. Beaton, "Advances in Enzyme and Membrane Technology," Institute of Chemical Engineers Symposium Series No. 51, Institute of Chemical Engineers, London, 1977, pp. 59—70. 

Schwuger MJ, Bartnik FG. Interaction of anionic surfactants with proteins, enzymes and membranes, in Anionic Surfactants (Gloxhuber C, ed.), Marcel Dekker, New York, 1980, pp. 1—49. 

Also when resorting to heuristic rate equations or other approximative schemes, the construction of detailed kinetic models necessitates quantitative knowledge about the kinetic properties of the involved enzymes and membrane transporters. Notwithstanding the formidable progress in experimental accessibility of system variables, detailed in Sections IV and VI, for most metabolic systems such quantitative information is only scarcely available. 

Equation (118) provides the conceptual basis for all subsequent considerations The nonzero elements of the matrices A and 0% define the new parameter space of the system, that is, the possible dynamic behavior of the system is evaluated in terms of these new parameters. Crucial to the analysis, the elements of both matrices have a well-defined and straightforward interpretation in biochemical terms, making their evaluation possible even in the face of incomplete knowledge about the detailed kinetic parameters of the involved enzymes and membrane transporters. Any further evaluation now rest on a careful interpretation of the two parameters matrices. 

As with other multisubunit enzymes (e.g., allosteric enzymes), the structural integrity of a membrane-bound enzyme primarily is maintained by noncovalent interactions such as hydrogen bonding, electrostatics, and hydrophobic interactions. Hydrophobic polypeptides (or hydrophobic portions of polypeptides) apparently are used to anchor the enzymes to the membrane through interactions with phospholipids. Therefore, I would characterize the interaction between the enzyme and membrane as chemical in nature rather than as geometric. ... 

The trans form of the molecule is more stable than the cis but will still fit onto many of the sites on the enzymes and membrane structures of the cells. When it does this, it blocks the sites and prevents the normal reactions of the cis molecules, which would usually be accepted at these sites. Trans fatty acids have been implicated in adverse health warnings. They are believed to be... 

Figure 2.26. Overview of the induction of cytochrome P450 3A4. A drug (D) binds to the pregnane X receptor (PXR) the complex moves to the nucleus, recruits additional proteins (otdy one of which is shown) and binds to specific regulatory sites on the DNA. This will induce transscription of CYP 3A4 ttiRNA, as well as other proteins such as conjugating enzymes and membrane transport proteins.

Ranjekar PK, Hinge A, Hegde MV, Ghate M, Kale A, Sitasawad S, et al. Decreased antioxidant enzymes and membrane essential polyunsaturated fatty acids in schizophrenia and bipolar mood disorder patients. Psychiatry Res. 2003 121 109-122. 

Plants as well as other organisms have evolved several adaptive strategies to counter these types of abiotic stresses (Csonka, 1989 Bohnert et al., 1995). At the cellular level, the most common type of osmotic adaptation is the accumulation of compatible solutes in the cytoplasm and the sequestration of NaCl into the vacuole (Rhodes and Hanson 1993 Bohnert et al., 1995). Compatible solutes arc small molecules that can act as nontoxic cytoplasmic osmolytes to raise osmotic pressure, and stabilize enzymes and membranes against damage by high salt levels (Wyn Jones, 1984). 

Fig. 16 a-d Schematic representation of polymer nanoreactors, a Cross section of triblock copolymer vesicle, b Polymersome with encapsulated enzyme and membrane-embedded channel protein. In the case described in the text, the substrate entering the vesicle is ampicillin, and the product of the hydrolysis is ampicillinoic acid, c Polymersome with embedded ionophores allowing Ca2+ ions to enter the vesicle ere they react with phosphate ions to form calcium phosphate crystals, d The LamB protein serves as a receptor to the 1 phage virus which can inject its DNA through the channel into the polymersome [259]. Reproduced with permission of The Royal Society of Chemistry... 

U. Kragl, Immobilized Enzymes and Membrane Reactors, in T. Godfrey, S. West (eds.), Industrial Enzymology, Macmillan Press, London, 19%, 275-283. 

The term "hyperplastic toxicity" is used in this presentation to describe toxicity-induced cell proliferation associated with increased mitotic activity, increased DNA (as judged by increased density of nuclear chromatin staining or indicia of increased DNA synthesis) and other changes associated with enzyme and membrane functions which are not of a malignant nature per se. 

Kragl, U., Immobilized enzymes and membrane reactor, in Industrial Enzymology, Godfrey, T. and Wet, S., Eds., Macmillan Press, London, U.K., 1996. 

Potential limitations include the tendency for primary cells in culture to dedifferentiate and lose functional expression of enzymes and membrane transporters during the course of culture. For example, expression of enzymes important for drug metabolism, such as CYPs, tends to readily decrease if culture conditions are not optimized. Plasma membrane transporters, such as many of the OATs, can readily internalize and become nonfunctional dining the course of cultme (Lash et al, 2006). Our strategy to counteract these potential problems has been to use the serum-free, hormonally defined medium that has become standard with primary culture of epithelial cells and then add other supplements to optimize maintenance of differentiated fnnction (Lash et al., 1995 Lash, 2012). 

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